JP5063645B2 - Digital watermark detection apparatus and digital watermark detection program - Google Patents

Description

The present invention is, with respect to paper and electronically displayed document or image is embedded an electronic watermark, later that by detecting the electronic watermark, electronic watermark you detect whether they document or image has been tampered The present invention relates to a detection device and a digital watermark detection program.

Conventionally, there has been a technique for detecting whether or not a document or image has been tampered with by embedding a digital watermark in a document or image displayed on paper or electronically and detecting the digital watermark later.
For example, Patent Document 1 discloses a technique for calculating a hash value of original image data and storing it using a digital watermark or the like, and comparing it with a hash value obtained from scanned image data later to detect falsification. It is disclosed. In Non-Patent Document 1, a bit called a visual hash is generated by using positive and negative correlations between an original image and a plurality of random Gaussian signals and stored using a digital watermark or the like. There has been disclosed a technique for detecting tampering by comparing with visual hash bits obtained from positive and negative correlations with the same plurality of random Gaussian signals.

JP 2006-222788 A

Fridrich, Jiri, “Visual Hash For Oblivious Watermarking”, Proc.SPIE Vol.3971, p.286-294, Security and Watermarking of Multimedia Contents II, Ping Wah Wong; Edward J. Delp; Eds.

However, for example, in the conventional image verification apparatus as described in Patent Document 1, the original image and the scanned image are printed even when there is no alteration due to the analog conversion noise generated when the original image is printed and further scanned. There is a problem in that the respective hash values do not always match and it is not possible to effectively detect tampering.
In addition, in the digital watermark embedding method as described in Non-Patent Document 1, it is necessary to create and store bit strings called visual hashes as many as the number of random Gaussian signals for which the correlation is calculated. Needs to increase the number of random Gaussian signals for which the correlation is calculated. In order to detect tampering, it is necessary to embed and store these visual hash bits with a digital watermark, which increases the number of embedded bits as a digital watermark.

The present invention has been made to solve the above problems, it is possible to effectively detect tampering, and child watermark detection apparatus and electrodeposition can be reduced the number of embedded bits as an electronic watermark An object is to obtain a digital watermark detection program.

The digital watermark detection apparatus according to the present invention scans a reference image generation unit that generates a plurality of reference images formed from different signals, a reference image generated by the reference image generation unit, and a digital watermark embedded image Information bit determining means for calculating a numerical value indicating a relationship with the scanned image and determining an information bit value corresponding to the reference image to 0 or 1 based on the numerical value;
Sum check bit detection means for detecting a digital watermark from the scanned image and detecting the sum check bit embedded as the digital watermark, the information bit obtained from the information bit determination means, and the sum check bit detection means Error detection / correction decoding means for performing error detection / correction decoding using the sum check bit and tampering determination means for determining whether the scanned image has been falsified from the error detection / correction result of the error detection / correction decoding means It is.

The digital watermark detection apparatus of the present invention performs error detection / correction encoding on 0 or 1 information bits based on the relationship between an original image and a reference image, and converts the sum check bits encoded by the error detection / correction encoding means into electronic Since the watermark is used to embed the original image, the presence / absence of tampering can be detected effectively based on the digital watermark.

1 is a configuration diagram illustrating a digital watermark embedding device according to a first embodiment of the present invention. It is a flowchart which shows operation | movement of the electronic watermark embedding apparatus by Embodiment 1 of this invention. It is a block diagram which shows the digital watermark detection apparatus by Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the digital watermark detection apparatus by Embodiment 1 of this invention. It is explanatory drawing which shows the operation | movement of the alteration detection of the digital watermark embedding apparatus and digital watermark detection apparatus by Embodiment 1 of this invention. It is explanatory drawing which shows the example of the error correction detection by the zero padding of the digital watermark embedding apparatus and digital watermark detection apparatus by Embodiment 1 of this invention. It is a block diagram which shows the electronic watermark embedding apparatus by Embodiment 2 of this invention. It is a block diagram which shows the digital watermark detection apparatus by Embodiment 2 of this invention. It is explanatory drawing which shows the example of the error correction detection by CRC calculation of the digital watermark embedding apparatus and digital watermark detection apparatus by Embodiment 2 of this invention.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a digital watermark embedding device according to Embodiment 1 of the present invention.
1 includes a Gaussian noise image generation unit 1, an original image acquisition unit 2, a vector inner product calculation unit 3, an information bit value calculation unit 4, a bit padding unit 5, an error detection / correction encoding unit 6, a thumb A check bit acquisition unit 7 and a digital watermark embedding unit 8 are provided.

  The Gaussian noise image generation unit 1 is a reference image generation unit that generates a plurality of images formed from different signals. The original image acquisition unit 2 is a means for acquiring a document or image (hereinafter referred to as an original image) displayed on paper or electronically, and includes a document data interface, a scanner, and the like. The vector inner product calculation unit 3 is a means for calculating a vector inner product between each Gaussian noise image generated by the Gaussian noise image generation unit 1 and the original image acquired by the original image acquisition unit 2. The information bit value calculation unit 4 is information bit determination means that calculates 1 or 0 information bits from the inner product value calculated by the vector inner product calculation unit 3. The bit padding unit 5 is a means for performing zero padding on the information bits calculated by the information bit value calculation unit 4 (adding bits having a value of 0 by a certain number of bits). The error detection / correction encoding unit 6 is error detection / correction encoding means for performing error detection / correction encoding of the information bits zero-padded by the bit padding unit 5. The sum check bit acquisition unit 7 is means for acquiring sum check bits when the error detection / correction encoding unit 6 performs error detection / correction encoding. The digital watermark embedding unit 8 embeds the sum check bit acquired by the sum check bit acquisition unit 7 as a digital watermark with respect to the original image acquired by the original image acquisition unit 2, and the digital watermark embedded image 100 is embedded. Is a digital watermark embedding means for outputting.

Next, the operation of the digital watermark embedding apparatus according to the first embodiment will be described.
The outline of the operation in the digital watermark embedding apparatus is as follows. That is, vector inner product calculation is performed between a plurality of different Gaussian noise images and one original image to generate information bits having the same number of bits as the number of Gaussian noise images. The information bits are zero-padded and then subjected to error detection and correction coding to obtain a certain number of sum check bits. An image in which the sum check bit thus obtained is embedded in an original image using a digital watermark is generated, and then a digital watermark embedded image 100 is generated.

Details of the digital watermark embedding process in the digital watermark embedding apparatus will be described below with reference to the flowchart of FIG.
For example, the original image acquisition unit 2 acquires print image data generated electronically from, for example, a word processing document, and then A pixel × B pixel (L _A × L _B in the size (length) when printed): unit mm) partial images are divided into N (steps ST101 and ST102).
For example, the Gaussian noise image generation unit 1 generates M Gaussian noise images in which pixel values are determined using Gaussian noise (step ST103). The size of the image is A pixel × B pixel. In order to determine the pixel value with Gaussian noise, for example, a Gaussian noise generation function that is a computer program may be used. At that time, the initial value of the Gaussian noise generation function is randomly changed for each image so that the Gaussian noise values generated thereafter are different from each other for the M Gaussian noise images.

The vector dot product calculation unit 3 calculates a vector dot product of each of the N partial images acquired by the original image acquisition unit 2 and the M Gaussian noise images generated by the Gaussian noise image generation unit 1. (Step ST104). For example, an average value of all pixel values is obtained for a partial image of the original image, and a difference between the average value and each current pixel value is set as a new pixel value. For example, in the partial image whose average pixel value is 128, the pixel value that was 100 is converted to -28, and the pixel value that was 200 is converted to 72. Similarly, an average value is calculated for each of M Gaussian noise images, and pixel values are converted. The pixel values (A × B) of the Gaussian noise image generated in this way are considered as [A × B] -dimensional vectors, and (X ₀ , X ₁ , X ₂ ,..., X _{A × B−1} ) Similarly, the pixel value (A × B) of the partial image is considered as an [A × B] -dimensional vector and is considered as (Y ₀ , Y ₁ , Y ₂ ,..., Y _{A × B−1} ). At this time, when the calculation result of the vector inner product of the Gaussian noise image m and the partial image of the original image is S, S _m = [X ₀ × Y ₀ + X ₁ × Y ₁ + X ₂ × Y ₂ +... + X _{A × B −1} × Y _{A × B−1} ].

For example, the information bit value calculation unit 4 calculates 1 as the information bit value if the vector inner product value S _m > 0 of the M Gaussian noise images m, and 0 if S _m <0. By performing this with M Gaussian noise images for one partial image n, M information bit values T ₀ , T ₁ , T ₂ ,..., T _M−1 are generated (step ST105). .
The bit padding unit 5 adds _C bit values U _C having a value of 0 to the _M information bit values T ₀ , T ₁ , T ₂ ,. coded bits sequence _{T 0, T 1, T 2} , ... · T M-1, U 0, U 1, ..., to generate the _{U C-1} (where _{U 0, U 1, ...,} U C-1 = 0) (step ST106).

ECC encoding section 6, [M + C] bits sequence _{T 0, T 1, T 2} , ..., T M-1, U 0, U 1, ..., error detection correction code to _{U C-1} And D sum check bits V ₀ , V ₁ ,..., V _D−1 are calculated (step ST 107).
The sum check bit acquisition unit 7 acquires D sum check bits V ₀ , V ₁ ,..., V _D−1 .
The digital watermark embedding unit 8 embeds the D sum check bits V ₀ , V ₁ ,..., V _D-1 , for example, in the region of the partial image n in the original image by using a digital watermark technique. Image data converted from the partial image is generated (step ST108). This is performed, for example, for all N partial images in the original image (step ST109), and the digital watermark embedded image 100 is generated.

  As described above, the digital watermark embedding apparatus converts the sign of the correlation between the original image and Gaussian noise into information bits 0/1. This information bit has the property that almost no bit inversion occurs for minute image fluctuations such as analog noise, and not a few bit inversions occur in the case of large image fluctuations assumed by artificial alteration (for example, Non-Patent Document 1). Therefore, the setting value of the error correction capability by the sum check bit is determined to be a value that “the minute bit inversion caused by analog noise can be completely corrected, but the bit inversion to the extent caused by artificial alteration cannot be corrected”. To do. This value is appropriately determined based on the required tampering detection accuracy and the like. In this way, by setting the error correction capability setting value to an appropriate value, it is possible to determine whether tampering has been detected based on the success or failure of error correction.

Next, the digital watermark detection apparatus in Embodiment 1 will be described.
FIG. 3 is a configuration diagram illustrating the digital watermark detection apparatus according to the first embodiment.
3 includes a Gaussian noise image generation unit 1, a scan image acquisition unit 2a, a vector inner product calculation unit 3, an information bit value calculation unit 4, a bit padding unit 5, an error detection / correction decoding unit 6a, a sum check. A bit acquisition unit 7, a digital watermark detection unit 9, a padding bit extraction unit 10, and a tampering determination unit 11 are provided.

  The Gaussian noise image generation unit 1 is a reference image generation unit that generates a plurality of reference images formed from signals different from each other, like the Gaussian noise image generation unit 1 of the digital watermark embedding apparatus. The scanned image acquisition unit 2a is a means for acquiring a scanned image obtained by scanning the digital watermark embedded image 100. The vector dot product calculation unit 3 has the same function as the vector dot product calculation unit 3 of the digital watermark embedding device, and the reference image generated by the Gaussian noise image generation unit 1, the scan image obtained by the scan image acquisition unit 2a, and Is a means for calculating a numerical value indicating the relationship. The information bit value calculation unit 4 and the bit padding unit 5 are units having functions similar to those of the information bit value calculation unit 4 and the bit padding unit 5 of the digital watermark embedding device, respectively. The error detection / correction decoding unit 6a uses the information bits bit-padded by the bit padding unit 5 and the sum check bits obtained from the sum check bit acquisition unit 7 to perform error detection / correction decoding means. It is.

  The digital watermark detection unit 9 is means for detecting a digital watermark from the scan image acquired by the scan image acquisition unit 2a. The sum check bit acquisition unit 7 calculates the sum check bit output from the digital watermark detection unit 9. Sum check bit detection means to be acquired. The padding bit extraction unit 10 is means for extracting padding bits from the information bits that have been subjected to error detection / correction decoding by the error detection / correction decoding unit 6a. The falsification determination unit 11 is a falsification determination unit that determines whether or not a scan image has been falsified based on the padding bits extracted by the padding bit extraction unit 10.

  The digital watermark detection apparatus and the digital watermark embedding apparatus described above are each realized by a computer, and the Gaussian noise image generation unit 1 to the digital watermark embedding unit 8 in the digital watermark embedding apparatus or the Gaussian noise image generation unit in the digital watermark detection apparatus. 1 to falsification determination unit 11 includes software corresponding to each function and hardware such as a CPU and a memory for executing the software. Alternatively, some or all of the functional units of the digital watermark embedding device and the digital watermark detection device may be configured by hardware.

Next, the operation of the digital watermark detection apparatus according to the first embodiment will be described.
FIG. 4 is a flowchart showing digital watermark detection processing.
The scan image acquisition unit 2a acquires a scan image obtained by scanning a printed material on a paper medium with a scanner, while the original image acquisition unit 2 of the digital watermark embedding apparatus acquires the original image and generates a partial image. Are divided into partial images (steps ST201 and ST202). At this time, assuming that the scan image has the same size as the digital watermark embedded image 100 generated by the digital watermark embedding apparatus, the position and number of partial images generated by the scan image acquisition unit 2a are as shown in FIG. It is equal to the position and the number of partial images generated by the original image acquisition unit 2.
The Gaussian noise image generation unit 1 performs the same operation as the Gaussian noise image generation unit 1 in FIG. 1 to generate M Gaussian noise images (step ST203).

  The vector inner product calculation unit 3 uses the partial image of the original image generated by the original image acquisition unit 2 as one input in the vector inner product calculation unit 3 of the digital watermark embedding device in FIG. 1, whereas the vector inner product calculation unit 3 in FIG. The calculation unit 3 performs the same operation except that the partial image generated by the scan image acquisition unit 2a is one input. That is, a vector inner product calculation with M Gaussian noise images is performed on one partial image (step ST204). Moreover, the number of pixels of each partial image is the same.

The information bit value calculation unit 4 performs one partial image n from the Gaussian noise image and the scan image calculated by the vector dot product calculation unit 3 in the same procedure as the information bit value calculation unit 4 of the digital watermark embedding device. To determine [A × B] information bit values W ₀ , W ₁ , W ₂ ,..., WA _{× B−1} (step ST205). Further, the bit padding unit 5 has the same value as [A × B] information bit values W ₀ , W ₁ , W ₂ ,..., WA _{A × B−1} , similarly to the bit padding unit 5 of FIG. 0 and is added the C bits value _{Q C, [a × B +} C] coded bits sequence _{W 0, W 1, W 2} , ..., W a × B-1, Q 0, Q 1, ... generates a _{Q C-1} (where _{Q 0, Q 1, ...,} Q C-1 = 0) ( step ST 206).

The digital watermark detection unit 9 acquires a partial image from the scanned image acquisition unit 2a, and detects a digital watermark therefrom (step ST207). The sum check bit acquisition unit 7 obtains D sum check bits R ₀ , R ₁ ,..., R _D−1 when the digital watermark detection unit 9 detects the digital watermark from the partial image (step ST208).
ECC decoding section 6a, the information bit sequence _W 0 which is a bit padded by the bit padding section _{5, W 1, W 2,} ..., W A × B-1, Q 0, Q 1, ..., a _{Q C-1} , R _D-1 added by the _D checksum bits R ₀ , R ₁ ,..., R _D-1 acquired by the sum check bit acquisition unit 7, and a bit string W ₀ , W ₁ , W _{2 ,. 1} , Q ₀ , Q ₁ ,..., Q _C-1 , R ₀ , R ₁ ,..., R _D-1 , error detection correction decoding, and decoded bit string W ′ ₀ , W ′ _{1 , W '2, ..., W} ' a × B-1, Q '0, Q' 1, ..., Q 'C-1, R' 0, R '1, ..., R' and outputs the _D-1 ( Step ST209).

The padding bit extraction unit 10 includes bit sequences W ′ ₀ , W ′ ₁ , W ′ ₂ ,..., W ′ _{A × B−1} , Q ′ ₀ , Q ′ ₁ that have been subjected to error detection / correction decoding by the error detection / correction decoding unit 6a. _{, ..., Q 'C-1} , R' 0, R '1, ..., R' from _D-1, padding bits _{R '0, R' 1,} ..., extracts the R _'D-1 (step ST210) .
The tampering determination unit 11 determines whether the padding bits R ′ ₀ , R ′ ₁ ,..., R ′ _D−1 extracted by the padding bit extraction unit 10 are = 0 or ≠ 0. If there is, it is determined that the partial image n has not been tampered with. Such processing is performed until processing of all partial images is completed (step ST212). When processing of all partial images is completed, it is determined that the digital watermark embedded image 100 has not been tampered with. (Step ST213). On the other hand, if NO in step ST211, it is determined that partial image n has been tampered with (step ST214).

FIG. 5 shows an alteration detection operation by such a digital watermark embedding device and a digital watermark detection device.
FIG. 6 is an example of detection of erroneous correction using zero padding by the digital watermark embedding apparatus and the digital watermark detection apparatus.
Hereinafter, the description will be made in correspondence with the numbers in parentheses in FIG.
(1) is an original image acquired by the original image acquisition unit 2 of the digital watermark embedding apparatus.
(3) is a Gaussian noise image generated by the Gaussian noise image generator 1.
(2) is a vector dot product calculation performed by the vector dot product calculation unit 3.
(4) is information bit calculation and zero padding performed by the information bit value calculation unit 4 and the bit padding unit 5.
(5) shows an error detection / correction encoding operation performed by the error detection / correction encoding unit 6.
(6) shows digital watermark embedding of the sum check bit performed by the digital watermark embedding unit 8.
Hereinafter, the operations after (7) are performed by the digital watermark detection apparatus.

(8) is a scan image acquired by the scan image acquisition unit 2a in the digital watermark detection apparatus.
(10) is a Gaussian noise image generated by the Gaussian noise image generator 1.
(9) is a vector dot product calculation performed by the vector dot product calculation unit 3.
(11) is information bit calculation and 0 padding performed by the information bit value calculation unit 4 and the bit padding unit 5.
(7) shows detection of a digital watermark performed by the digital watermark detection unit 9 and acquisition of a sum check bit by the sum check bit acquisition unit 7.
(12) indicates error detection / correction decoding performed by the error detection / correction decoding unit 6a.
(13) shows extraction of padding bits from the bit string of the error detection / correction decoding result performed by the padding bit extraction unit 10 and tampering determination performed by the tampering determination unit 11. If it is corrected correctly, it is determined that there is no tampering, and if it is erroneously corrected, it is determined that there is tampering. That is, as shown in the decoding result of FIG. 6, if the correction is not correct in the error detection / correction decoding unit 6a, the padding bits include bits that are not ≠ 0. Thereby, it can be determined that tampering has been performed.

  In the above embodiment, 0 is used as the padding bit in the bit padding unit 5, but 1 may be added to all. In this case, in the digital watermark detection apparatus, when the padding bits extracted by the padding bit extraction unit 10 are not ≠ 1, the tampering determination unit 11 determines that tampering has been performed.

  As described above, according to the digital watermark embedding device of the first embodiment, the reference image generation unit that generates a plurality of images formed from different signals, the original image, and the reference generated by the reference image generation unit Based on the calculation result of the numerical value indicating the relationship with the image, information bit determining means for determining the information bit corresponding to the reference image to 0 or 1, and a plurality of information bits determined by the information bit determining means for error detection and correction code Error detection / correction encoding means, and a digital watermark embedding means for embedding a sum check bit encoded by the error detection / correction encoding means in an original image using a digital watermark to generate a watermark embedded image Therefore, tampering can be detected effectively, and the number of embedded bits as a digital watermark can be reduced.

  Further, according to the digital watermark detection apparatus of the first embodiment, the reference image generation unit that generates a plurality of reference images formed from different signals, the reference image generated by the reference image generation unit, and the digital watermark embedding A numerical value indicating a relationship with the scanned image obtained by scanning the completed image, and an information bit determining means for determining an information bit value corresponding to the reference image to 0 or 1 based on the numerical value, and detecting a digital watermark from the scanned image The sum check bit detecting means for detecting the sum check bit embedded as the digital watermark, the information bit obtained from the information bit determining means, and the sum check bit obtained from the sum check bit detecting means The error detection / correction decoding means for performing error detection / correction decoding and the error detection / correction result of the error detection / correction decoding means Since a tamper determining unit determines the presence or absence of falsification of the image can be based on the electronic watermark embedded by the electronic watermark embedding apparatus of the first embodiment, to detect the presence or absence of reliable tamper.

  In addition, according to the digital watermark embedding device of the first embodiment, the information bit determining means calculates the correlation between the original image and a plurality of random Gaussian signals, and determines the information bit to be 0 or 1 based on the sign. Therefore, information bits for effective tampering detection can be obtained.

  Also, according to the digital watermark detection apparatus of the first embodiment, the information bit determining means calculates the correlation between the scanned image and the random Gaussian signal, and determines the information bit to be 0 or 1 based on the sign. It can be an information bit for effective tampering detection.

  Further, according to the digital watermark embedding apparatus of the first embodiment, the error detection / correction encoding means adds a plurality of bits of all 0s or all 1s to a plurality of information bits determined by the information bit determination means. Since the error detection / correction encoding is performed, the accuracy of the falsification determination can be improved.

  Further, according to the digital watermark detection apparatus of the first embodiment, the error detection / correction decoding unit adds a plurality of bits of all 0s or all 1s to the information bits obtained from the information bit determination unit, and then adds the sum check bits. Since the error detection correction decoding is performed using the sum check bit obtained from the detection means, the accuracy of tampering determination can be improved.

  Further, according to the digital watermark embedding program of the first embodiment, the computer that embeds the digital watermark in the original image, the reference image generation means for generating a plurality of images formed from different signals, the original image, and the reference image Based on the calculation result of the numerical value indicating the relationship with the reference image generated by the generating means, an information bit determining means for determining the information bit corresponding to the reference image to 0 or 1, and a plurality of information bits determined by the information bit determining means Error detection / correction encoding means for error detection / correction encoding of information bits and sum check bits encoded by the error detection / correction encoding means are embedded in the original image using a digital watermark to generate a watermark embedded image Since it is made to function as a digital watermark embedding means, tampering can be detected effectively, and embedding as a digital watermark is possible. The electronic watermark embedding apparatus which can reduce the number of write bits can be realized on a computer.

  Further, according to the digital watermark detection program of the first embodiment, the computer that detects the digital watermark from the digital watermark embedded image, the reference image generation unit that generates a plurality of reference images formed from different signals, and the reference A numerical value indicating the relationship between the reference image generated by the image generating means and the scanned image obtained by scanning the digital watermark embedded image is calculated, and the information bit value corresponding to the reference image is determined to be 0 or 1 based on the numerical value. Information bit determination means, sum check bit detection means for detecting a digital watermark from the scanned image and detecting a checksum bit embedded as the digital watermark, information bits obtained from the information bit determination means, and sum check Perform error detection / correction decoding using sum check bit obtained from bit detection means This is realized by the digital watermark embedding program according to the first embodiment because it functions as a falsification determination unit that determines whether or not a scanned image has been falsified from the error detection correction result of the error detection / correction decoding unit. An electronic watermark detection apparatus that can reliably detect the presence or absence of tampering based on the electronic watermark embedded by the electronic watermark embedding apparatus can be realized on a computer.

Embodiment 2. FIG.
In the first embodiment, the digital watermark embedding device embeds the sum check bit generated by padding 0 or 1 bit and then performing error detection and correction coding with the digital watermark, and the digital watermark detection device uses the 0 or 1 bit. Bits were subjected to error detection correction decoding from the padding bits and the sum check bits detected from the digital watermark, and if the padded bits were corrected, it was determined that the partial image was falsified. On the other hand, in the second embodiment, the digital watermark embedding apparatus performs CRC (Cyclic Redundancy Check) operation on the information bits to obtain the CRC output value, and then combines the information bit and the CRC output value. The bit string is subjected to error detection / correction encoding to obtain a sum check bit, and both the CRC output value and the error detection / correction encoding sum check bit are embedded with a digital watermark.
In the digital watermark detection apparatus of the second embodiment, the CRC output value extracted from the digital watermark and the sum check bit of error detection / correction encoding are added to the information bit, and then error detection / correction decoding is performed, and further correction is performed. It is determined whether or not the information bits and the CRC output value are correctly corrected by performing a CRC operation using the information bits and the CRC output value.

FIG. 7 is a configuration diagram illustrating the digital watermark embedding apparatus according to the second embodiment.
The illustrated digital watermark embedding device includes a Gaussian noise image generation unit 1, an original image acquisition unit 2, a vector inner product calculation unit 3, an information bit value calculation unit 4, an error detection / correction encoding unit 6b, a sum check bit / CRC bit acquisition unit. 7a, a digital watermark embedding unit 8a, and a CRC calculation unit 12. Here, since the Gaussian noise image generation unit 1 to the information bit value calculation unit 4 are the same as the configuration of the digital watermark embedding device of the first embodiment, description thereof is omitted here.

  The CRC calculation unit 12 is a CRC calculation unit that performs CRC calculation on a plurality of information bits determined by the information bit value calculation unit 4 to obtain a CRC output value. The error detection / correction encoding unit 6b performs error detection / correction encoding on a bit string that is a combination of the information bits determined by the information bit value calculation unit 4 and the CRC output value calculated by the CRC calculation unit 12, and performs summing. This is error detection and correction encoding means for obtaining check bits. The sum check bit / CRC bit acquisition unit 7a is means for acquiring the sum check bit obtained by the error detection / correction encoding unit 6b and the CRC calculation value calculated by the CRC calculation unit 12. The digital watermark embedding unit 8a obtains the original image by using the digital watermark for the sum check bit obtained by the sum check bit / CRC bit obtaining unit 7a and the CRC check value encoded by the error detection / correction coding unit 6b. This is a digital watermark embedding unit that embeds the original image acquired by the unit 2 and generates the digital watermark embedded image 101.

Next, the operation of the digital watermark embedding apparatus according to the second embodiment will be described.
Since the operation until the information bit value calculation unit 4 obtains a plurality (M) of information bit values is the same as that of the digital watermark embedding apparatus of the first embodiment, the description thereof is omitted. The CRC calculation unit 12 performs CRC calculation on the M information bit values T ₀ , T ₁ , T ₂ ,..., T _M−1 , and outputs c-bit CRC output values u ₀ , u ₁ ,. _C-1 is obtained. Then, the error detecting and correcting coding section 6b, [M + c] bits string _{t 0, t 1, t 2} , ..., t M-1, u 0, u 1, ..., error with respect to _{u C-1} Detection correction encoding is performed, and d sum check bits v ₀ , v ₁ ,..., V _d−1 are calculated. Checksum bits / CRC bit acquiring unit 7a, c number of CRC output values _{u 0, u 1, ...,} a _{u C-1,} d pieces of checksum bits _{v 0, v 1, ...,} a _{v d-1} get. Electronic watermark embedding unit 8a, the c-number of CRC output values _{u 0,} u 1, _..., a _{u C-1,} d pieces of checksum bits _{v 0,} v 1, _..., a _{v d-1,} for example, the original Image data converted from the partial image is generated by embedding it in the region of the partial image n in the image using the digital watermark technique. This is performed, for example, for all N partial images in the original image, and the digital watermark embedded image 101 is generated.

Next, a digital watermark detection apparatus according to Embodiment 2 will be described.
FIG. 8 is a configuration diagram illustrating the digital watermark detection apparatus according to the second embodiment.
The illustrated digital watermark detection apparatus includes a Gaussian noise image generation unit 1, a scan image acquisition unit 2a, a vector inner product calculation unit 3, an information bit value calculation unit 4, an error detection / correction decoding unit 6c, a sum check bit / CRC bit acquisition unit 7b. A digital watermark detection unit 9, a CRC calculation unit 12a, and a falsification determination unit 11a.

  Here, since the Gaussian noise image generation unit 1 to the information bit value calculation unit 4 and the digital watermark detection unit 9 have the same configuration as that of the digital watermark detection apparatus according to the first embodiment, description thereof is omitted here. The sum check bit / CRC bit acquisition unit 7a is means for obtaining a sum check bit and a CRC output value from the digital watermark detected by the digital watermark detection unit 9. The error detection / correction decoding unit 6c uses the information bits obtained from the information bit value calculation unit 4 and the sum check bits and CRC output values obtained by the sum check bit / CRC bit acquisition unit 7a to perform error detection / correction decoding. It is an error detection correction decoding means for performing. The CRC calculation unit 12a, based on the calculation result of the CRC calculation performed using the information bits corrected by the error detection / correction decoding unit 6c and the CRC output value, and the CRC in the error detection / correction decoding unit 6c Correction determination means for determining whether or not the output value is correctly corrected. The falsification determination unit 11a is a falsification determination unit that determines whether the scanned image has been falsified based on the determination result of the CRC calculation unit 12a.

  Note that each of the digital watermark embedding device and the digital watermark detection device according to the second embodiment is also realized by a computer, and the Gaussian noise image generation unit 1 to the digital watermark embedding unit 8a in the digital watermark embedding device or the digital watermark detection device. The Gaussian noise image generation unit 1 to falsification determination unit 11a are composed of software corresponding to each function and hardware such as a CPU and a memory for executing the software. Alternatively, some or all of the functional units of the digital watermark embedding device and the digital watermark detection device may be configured by hardware.

The operation of the digital watermark detection apparatus according to the second embodiment will be described below.
The generation of a plurality (M) of Gaussian noise images in the Gaussian noise image generation unit 1 is the same as the operation of the digital watermark detection apparatus of the first embodiment. The operation of the scanned image acquisition unit 2a is the same as that of the digital watermark detection apparatus of the first embodiment and the digital watermark embedding apparatus of the second embodiment. That is, the scan image acquisition unit 2a acquires a scan image obtained by scanning a printed material on a paper medium with a scanner, while the original image acquisition unit 2 in FIG. 7 acquires the original image and generates a partial image. Is divided into partial images. At this time, assuming that the scanned image has the same size as the digital watermark embedded image 101 generated by the digital watermark embedding apparatus in FIG. 7, the position and number of partial images generated by the scanned image acquisition unit 2a are It is equal to the position and number of partial images generated by the original image acquisition unit 2 in FIG.

The vector inner product calculation unit 3 uses the partial image of the original image generated by the original image acquisition unit 2 as one input in the vector inner product calculation unit 3 of FIG. 7, whereas the partial image generated by the scan image acquisition unit 2a. Is one of the inputs, and the operation is the same except for this point. Moreover, the number of pixels of each partial image is the same.
The information bit value calculation unit 4 performs the process for one partial image n from the Gaussian noise image and the scan image calculated by the vector dot product calculation unit 3 in the same procedure as the information bit value calculation unit 4 in FIG. Thus, [A × B] information bit values W ₀ , W ₁ , W ₂ ,..., W _{A × B−1} are determined.

The digital watermark detection unit 9 detects a digital watermark from the image acquired by the scan image acquisition unit 2a, as in the digital watermark detection apparatus of the first embodiment.
Checksum bits / CRC bit acquiring unit 7a, by digital watermark detection unit 9 detects an electronic watermark from partial images, d number of checksum bits _{r 0,} r 1, and ··· _{r d-1,} c Bit CRC output values u ₀ , u ₁ ,..., U _C−1 are obtained.
The error detection / correction decoding unit 6c acquires the information bit string W ₀ , W ₁ , W ₂ ,..., WA _{× B−1} calculated by the information bit value calculation unit 4 by the sum check bit / CRC bit acquisition unit 7a. has been CRC output values _{u 0, u 1, ...,} u C-1 and checksum bits _{r 0,} r 1, _..., a _{r d-1} Tokyo, bit string _{W 0, W 1, W 2} , ..., W A _{× B−1} , u ₀ , u ₁ ,..., U _C−1 , r ₀ , r ₁ ,..., Rd ₋₁ , error detection correction decoding, and decoded bit string w ′ ₀ , _{w '1, w' 2,} ..., w 'a × B-1, q' 0, q '1, ..., q' C-1, r '0, r' 1, ..., a r _'d-1 Generate.

The CRC calculation unit 12a performs the error detection / correction decoding by the error detection / correction decoding unit 6c w ′ ₀ , w ′ ₁ , w ′ ₂ ,..., W ′ _{A × B−1} , q ′ ₀ , q ′ ₁ ,. , Q ′ _C−1 , r ′ ₀ , r ′ ₁ ,..., R ′ _d−1 , w ′ ₀ , w ′ ₁ , w ′ _{2 ,. 1} is extracted and a CRC operation is performed to calculate the generated CRC output values q ″ ₀ , q ″ ₁ ,..., Q ″ _C−1 .The generated CRC output values q ″ ₀ , q ″ ₁ ,. q ″ _C−1 is compared with q ′ ₀ , q ′ ₁ ,..., q ′ _C−1 calculated by the error detection / correction decoding unit 6c, and if they match, the error detection / correction decoding unit 6c correctly corrects them. to decide. If they do not match, it is determined that they were not corrected correctly.
The tampering determination unit 11a determines that there has been no tampering when it is determined that the CRC calculation unit 12a has correctly corrected the tampering. If it is determined that the correction has not been made correctly, it is determined that there has been falsification.

  FIG. 9 shows an example of error correction detection using CRC calculation in the digital watermark embedding apparatus and the digital watermark detection apparatus according to the second embodiment of the present invention. As shown in the figure, when an error is included in information bits, the CRC output values do not match, and in such a case, the falsification determining unit 11a determines that falsification has occurred.

In the second embodiment, the number of bits to be embedded using the digital watermark is all the bits of the sum check bit and all the bits of the CRC output value. However, the number of bits is smaller than that of embedding the information bits with the digital watermark. There is an effect.
Further, the number of bits extracted by detecting the digital watermark is all the bits of the sum check bits and all the bits of the CRC output value. However, the number of bits can be reduced as compared with the case where the information bits are detected by the digital watermark. There is an effect.

  In the second embodiment, the digital watermark embedding apparatus performs error detection / correction coding on the bit string that is a combination of the information bit value and the CRC output value, and the digital watermark detection apparatus extracts the information bit value extracted from the digital watermark. After the CRC output value is subjected to error detection / correction decoding, a CRC operation is performed on the information bit value and compared with the extracted CRC output value. Therefore, whether or not the information bit value has been correctly decoded by error detection / correction decoding is accurately determined. There is an effect that it can be judged.

  Furthermore, since it is sufficient to embed a small number of bits with a digital watermark rather than embedding information bits with a digital watermark, the image quality of an image embedded with a digital watermark is less likely to deteriorate. In addition, since the number of bits to be embedded or detected with a digital watermark can be reduced, there is an effect that it can be realized with a relatively simple digital watermark technique. In addition, since the number of bits to be detected is small, the detection accuracy can be improved.

  In the second embodiment, the CRC output value embedded in the image may be embedded not only in the case of embedding all the bits generated by the CRC calculation unit 12 but also in some of the bits. In that case, in the digital watermark detection apparatus, the comparison of the CRC output value obtained by the CRC calculation and the CRC output value detected from the image is limited to only a part of the bits, and it is determined whether or not the correction is correctly performed. May have a lower accuracy, but has the advantage that fewer bits are embedded in the image.

  As described above, according to the digital watermark embedding device of the second embodiment, the reference image generation unit that generates a plurality of images formed from different signals, the original image, and the reference generated by the reference image generation unit CRC calculation for a plurality of information bits determined by the information bit determination means, information bit determination means for determining the information bit corresponding to the reference image to 0 or 1 based on the calculation result of the numerical value indicating the relationship with the image And CRC calculation means for obtaining the CRC output value, and error detection correction coding means for obtaining the sum check bit by performing error detection and correction coding on the bit string obtained by combining the information bits and the CRC output value; The sum check bit encoded by the error detection / correction encoding means and at least a part of the CRC output value are embedded in the original image using a digital watermark, Since a digital watermark embedding means for generating an order inclusive completed image, it is possible to effectively detect tampering, and can reduce the number of embedded bits as an electronic watermark.

  In addition, according to the digital watermark detection apparatus of the second embodiment, the reference image generation unit that generates a plurality of reference images formed from different signals, the reference image generated by the reference image generation unit, and the digital watermark embedding A numerical value indicating a relationship with the scanned image obtained by scanning the completed image, and an information bit determining means for determining an information bit value corresponding to the reference image to 0 or 1 based on the numerical value, and detecting a digital watermark from the scanned image Digital watermark detection means for detecting the sum check bit and CRC output value embedded as the digital watermark, information bits obtained from the information bit determination means, sum check bits and CRC obtained from the digital watermark detection means Error detection / correction decoding means for performing error detection / correction decoding using the output value and error detection / correction decoding means Correction determination means for determining whether or not the information bits and the CRC output value are correctly corrected by the error detection and correction decoding means based on the calculation result of the CRC calculation performed using the information bits and the CRC output value And a falsification determination unit that determines whether or not the scanned image has been falsified based on the determination result of the correction determination unit, so that it is ensured based on the digital watermark embedded by the digital watermark embedding device of the second embodiment. The presence or absence of tampering can be detected.

  In addition, according to the digital watermark embedding device of the second embodiment, the information bit determining means calculates the correlation between the original image and a plurality of random Gaussian signals, and determines the information bit to be 0 or 1 based on the sign. Therefore, information bits for effective tampering detection can be obtained.

  Further, according to the digital watermark detection apparatus of the second embodiment, the falsification determination unit determines that the scan image has not been falsified when the error detection / correction decoding unit determines that the error detection / correction has been normally completed. When it is determined that the error detection / correction has not ended normally, it is determined that the scanned image has been tampered with, so that the accuracy of the tampering determination can be improved.

  Further, according to the digital watermark embedding program of the second embodiment, the computer that embeds the digital watermark in the original image, the reference image generation means for generating a plurality of images formed from different signals, the original image, and the reference image Based on the calculation result of the numerical value indicating the relationship with the reference image generated by the generating means, an information bit determining means for determining the information bit corresponding to the reference image to 0 or 1, and a plurality of information bits determined by the information bit determining means CRC calculation means for performing CRC operation on the information bits and obtaining the CRC output value, and error detection correction coding is performed on the bit string combining the information bits and the CRC output value to obtain the sum check bit. Error detection / correction encoding means, sum check bit encoded by error detection / correction encoding means, and at least part of CRC output value Since it is embedded in the original image using a child watermark and functions as a digital watermark embedding means for generating a watermark embedded image, tampering can be detected effectively, and the number of embedded bits as a digital watermark can be reduced. A digital watermark embedding apparatus that can be made small can be realized on a computer.

  Further, according to the digital watermark detection apparatus of the second embodiment, a computer that detects a digital watermark from a digital watermark embedded image, a reference image generation unit that generates a plurality of reference images formed from different signals, and a reference A numerical value indicating the relationship between the reference image generated by the image generating means and the scanned image obtained by scanning the digital watermark embedded image is calculated, and the information bit value corresponding to the reference image is determined to be 0 or 1 based on the numerical value. Information bit determination means, digital watermark detection means for detecting a digital watermark from the scanned image and detecting the sum check bit and CRC output value embedded as the digital watermark, and information bits obtained from the information bit determination means , Using the sum check bit and CRC output value obtained from the digital watermark detection means, Error detection and correction decoding means for performing error detection and correction decoding means, and information bits corrected and detected by the error detection and correction decoding means, and information bits obtained by the error detection and correction decoding means based on the result of CRC calculation performed using the CRC output value The correction determination means for determining whether or not the CRC output value is correctly corrected, and the falsification determination means for determining whether the scanned image has been falsified based on the determination result of the correct determination means. An electronic watermark detection apparatus that can reliably detect the presence / absence of tampering can be realized on a computer based on the electronic watermark embedded by the electronic watermark embedding apparatus realized by the electronic watermark embedding program of Embodiment 2. .

  1 Gaussian noise image generation unit, 2 original image acquisition unit, 2a scan image acquisition unit, 3 vector inner product calculation unit, 4 information bit value calculation unit, 5 bit padding unit, 6, 6b error detection correction encoding unit, 6a, 6c Error detection correction decoding unit, 7 sum check bit acquisition unit, 7a sum check bit / CRC bit acquisition unit, 8, 8a digital watermark embedding unit, 9 digital watermark detection unit, 10 padding bit extraction unit, 11, 11a falsification determination unit, 12, 12a CRC calculation unit, 100, 101 Digital watermark embedded image.

Claims (7)

Reference image generation means for generating a plurality of reference images formed from different signals;
  A numerical value indicating the relationship between the reference image generated by the reference image generating means and the scanned image obtained by scanning the digital watermark embedded image is calculated, and the information bit value corresponding to the reference image is set to 0 or 1 depending on the numerical value. Information bit determining means for determining
  Sum check bit detection means for detecting a digital watermark from the scanned image and detecting a sum check bit embedded as the digital watermark;
  Error detection correction decoding means for performing error detection correction decoding using the information bits obtained from the information bit determination means and the sum check bits obtained from the sum check bit detection means;
  An electronic watermark detection apparatus comprising: a tamper determination unit that determines whether a scan image has been tampered with based on an error detection correction result of the error detection correction decoding unit. 2. The digital watermark detection apparatus according to claim 1, wherein the information bit determining means calculates a correlation between the scanned image and the random Gaussian signal, and determines the information bit to be 0 or 1 based on the sign. The error detection / correction decoding means adds a plurality of bits of all 0s or all 1s to the information bits obtained from the information bit determination means, and then uses the sum check bits obtained from the sum check bit detection means to detect errors. The digital watermark detection apparatus according to claim 1, wherein correction decoding is performed. Reference image generation means for generating a plurality of reference images formed from different signals;
  A numerical value indicating the relationship between the reference image generated by the reference image generating means and the scanned image obtained by scanning the digital watermark embedded image is calculated, and the information bit value corresponding to the reference image is set to 0 or 1 depending on the numerical value. Information bit determining means for determining
  Digital watermark detection means for detecting a digital watermark from the scanned image and detecting a sum check bit and a CRC output value embedded as the digital watermark;
  Error detection / correction decoding means for performing error detection / correction decoding using the information bits obtained from the information bit determination means and the sum check bits and CRC output values obtained from the digital watermark detection means;
  Based on the calculation result of the CRC calculation performed using the information bits corrected and detected by the error detection and correction decoding means and the CRC output value, the information bits and the CRC output value are correctly set by the error detection and correction decoding means. Correction determination means for determining whether correction has been made,
  An electronic watermark detection apparatus comprising: a falsification determination unit that determines whether the scanned image has been falsified based on a determination result of the correction determination unit.   When the falsification determining means determines that the error detection correction decoding means that the error detection / correction has been normally completed, the falsification determining means determines that the scan image has not been falsified, and the error detection / correction is not normally completed. 5. The digital watermark detection apparatus according to claim 2, wherein it is determined that the scanned image has been tampered with. A computer that detects watermarks from embedded images
  Reference image generation means for generating a plurality of reference images formed from different signals;
  A numerical value indicating a relationship between the reference image generated by the reference image generating means and a scanned image obtained by scanning the digital watermark embedded image is calculated, and an information bit value corresponding to the reference image is set to 0 or 0 based on the numerical value. Information bit determining means for determining 1;
  Sum check bit detection means for detecting a digital watermark from the scanned image and detecting a sum check bit embedded as the digital watermark;
  Error detection correction decoding means for performing error detection correction decoding using the information bits obtained from the information bit determination means and the sum check bits obtained from the sum check bit detection means;
  An electronic watermark detection program for functioning as a falsification determination unit that determines whether a scan image has been falsified from an error detection correction result of the error detection correction decoding unit. A computer that detects watermarks from embedded images
  Reference image generation means for generating a plurality of reference images formed from different signals;
  A numerical value indicating a relationship between the reference image generated by the reference image generating means and a scanned image obtained by scanning the digital watermark embedded image is calculated, and an information bit value corresponding to the reference image is set to 0 or 0 based on the numerical value. Information bit determining means for determining 1;
  Digital watermark detection means for detecting a digital watermark from the scanned image and detecting a sum check bit and a CRC output value embedded as the digital watermark;
  Error detection / correction decoding means for performing error detection / correction decoding using the information bits obtained from the information bit determination means and the sum check bits and CRC output values obtained from the digital watermark detection means;
  Based on the calculation result of the CRC calculation performed using the information bits corrected and detected by the error detection and correction decoding means and the CRC output value, the information bits and the CRC output value are correctly set by the error detection and correction decoding means. Correction determination means for determining whether correction has been made,
  An electronic watermark detection program for functioning as a falsification determination unit that determines whether the scanned image has been falsified based on a determination result of the correction determination unit.

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