JP2006157547A - Method, device, and program for checking authenticity of printed matter by correlation type electronic watermark - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine a normal printed matter and a copied one of printed matters with high accuracy. <P>SOLUTION: An embedding printer P prints a correlation type electronic watermark in print data (step S11). Next, the normal printed matter to be reference is selected (step S21), a test normal printed matter is selected (step S22), an acquiring device S acquires these images (step S23), and a discrimination threshold T_ps is calculated on the basis of detection strength of electronic watermark detected from the acquired image data (step S24). The acquiring device S acquires images about printed matters of a determination target by using the discrimination threshold T_ps (step S31), reliability is calculated on the basis of the detection strength of the electronic watermark, the reliability is compared with the discrimination threshold T_ps to determine the authenticity of the printed matter. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method, an apparatus, and a program for checking the authenticity of printed matter printed by embedding correlated digital watermarks in print data.

2. Description of the Related Art Conventionally, digital watermarks have been used in order to determine illegally printed matter by taking a regular printed matter as image data using a scanner, digital camera, or the like. In this method, an electronic watermark is embedded in print data used for printing a regular product, and an authenticity check is performed based on whether or not the embedded electronic watermark is detected from image data obtained by scanning a printed matter to be determined.
Patent Documents 1 to 4 are known as conventional techniques.
Japanese Patent Laid-Open No. 10-250029 JP 2001-134672 A JP 2003-137348 A JP 2003-337683 A

  However, the conventional authenticity check based on the presence or absence of a digital watermark has made it difficult to detect a printed copy after finely scanning the printed matter. FIG. 7 is a graph of the number of blocks in which a digital watermark is detected from each of nine different images. The horizontal axis of the graph shows 9 types of images numbered and arranged, and the vertical axis shows the digital watermark detected when each image is divided into 100 blocks and each digital watermark is embedded. Represents the number of blocks created. The meaning of the graph legend is as follows. The “reference” is the number of blocks detected by scanning a regular printed material. “Regular” refers to detection by scanning a regular product in the same way as “reference”, but the number of detected blocks varies even with the same regular product. The average value of the detection results is shown. “Copy 1” is the number of blocks detected by scanning a genuine product and scanning a printed product. “Copy 2” is the number of blocks detected by scanning a regular product, performing image processing such as repairing a portion where the image quality has deteriorated, and scanning a printed product. According to this graph, although the number of detected blocks varies depending on the image, there are many cases where there is no significant difference in the number of detected blocks between the genuine product and copy product. Is difficult to distinguish.

FIG. 8 explains the above in detail and shows an example of the number of digital watermark detection blocks. These are a part of the printed material, but are divided into 20 blocks in total of 5 blocks vertically and 4 blocks horizontally, and the detection results from the printed material in which digital watermarks are embedded in each block are shown. The “regular product” is a detection result when a regular product is scanned. The meanings of “copy product 1” and “copy product 2” are the same as described above. “Copy of copy product” is a detection result when “copy product 1” is scanned and a printed product is scanned. In this way, there are blocks that are erroneously detected in “copy of copy product”, but even in the case of “copy product 1” and “copy product 2”, the digital watermark is correct in each block in the same way as “regular product”. May be detected.
SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and an object of the present invention is a method, apparatus, and program for checking the authenticity of a printed matter using a correlated electronic watermark, which can accurately determine a genuine product and a copy product. Is to provide.

  The present invention has been made to solve the above-described problems, and the invention according to claim 1 is based on a genuine product printed with print data in which a correlation type digital watermark is embedded and the genuine product. In a method for checking the authenticity of a printed matter for determining a counterfeit copy product, a first method for obtaining a discrimination threshold value based on a detection intensity of a digital watermark detected from the image data by capturing image data from the regular product by a capture device. A second step of acquiring image data from a printed matter to be checked for authenticity by the acquisition device, and obtaining a reliability based on a detection strength of a digital watermark detected from the image data, and the determination threshold value. And a third step of checking the authenticity of the printed matter by comparing the reliability and a method for checking the authenticity of the printed matter.

  According to a second aspect of the present invention, in the printed matter authenticity checking method according to the first aspect, in the first step, a reference regular product and one or a plurality of test regular products are selected to serve as the reference. A reliability is obtained based on the difference between the detection strength of the digital watermark detected from the genuine product and the detection strength of the digital watermark detected from the test genuine product, and a determination threshold value based on the average and standard deviation of the reliability It is characterized by calculating | requiring.

  According to a third aspect of the present invention, in the printed matter authenticity checking method according to the second aspect, the detection strength of the digital watermark detected from the reference genuine product is detected by selecting a plurality of reference genuine products. An average of detection intensities of the respective digital watermarks is used.

  According to a fourth aspect of the present invention, in the printed matter authenticity checking method according to any one of the first to third aspects, the reliability in the second step is the reliability of a digital watermark detected from a reference genuine product. It is obtained based on the difference between the detected intensity and the detected intensity of the digital watermark detected from the printed matter to be checked for authenticity.

  According to a fifth aspect of the present invention, there is provided: means for obtaining a discrimination threshold based on a detected intensity of a correlation type digital watermark detected from genuine image data captured by a capture device; and capture by the capture device And a means for obtaining a reliability based on the detected intensity of the correlation type digital watermark detected from the image data of the printed object to be checked for authenticity.

  According to a sixth aspect of the present invention, there is provided a process for obtaining a discrimination threshold based on a detected intensity of a correlation type digital watermark detected from genuine image data captured by a capture device, and captured by the capture device This is a program for causing a computer to execute processing for obtaining reliability based on the detected intensity of the correlation type digital watermark detected from the image data of the printed matter to be checked for authenticity.

According to the first, fifth, and sixth aspects of the present invention, it is possible to detect even a printed copy after finely scanning a printed matter that has been properly printed, and to improve the accuracy of checking the authenticity of the printed matter. Therefore, it can be expected to be effective in preventing and suppressing forgery of printed matter.
According to the second aspect of the present invention, even when there is a variation in the detection strength of the digital watermark detected from the genuine product, it is possible to obtain the discrimination threshold while suppressing this.
According to the third aspect of the present invention, even when there is a variation in the detection strength of the digital watermark detected from the regular product that is the reference, it is possible to obtain the discrimination threshold while suppressing this variation.
According to the fourth aspect of the present invention, the difference between the detected strength of the digital watermark detected from the reference regular product and the detected strength of the digital watermark detected from the printed material subject to the authenticity check is quantified and evaluated. be able to.

Embodiments of the present invention will be described below. First, an example of a digital watermark information embedding method and detection method for a correlation type digital watermark used in the authenticity check of a printed matter according to the present invention will be described. Next, the reliability of the detected digital watermark and the discrimination threshold will be described. .
First, an example of a method for embedding digital watermark information using a correlation type digital watermark will be described. Here, a function representing a value for each pixel in the embedding target image is In (x). This is because when printing data is divided into a plurality of blocks and a digital watermark is embedded for each block, for example, when one block is composed of N pixels (for example, P pixels horizontally and Q pixels vertically) When a number is assigned to each, x takes a value from 0 to N−1, and In (x) represents the value of the x-th pixel among N pixels. Further, the electronic watermark information is assumed to be w. The digital watermark information w is diffused into weak noise distributed over a wide band by spectrum spreading. In spreading the digital watermark information w, it is necessary to select an appropriate spreading sequence. As a spreading sequence, a sequence having a sharp autocorrelation with respect to the same signal and a small cross-correlation so as to distinguish between different signals is desirable so that synchronization can be easily established. For example, M length L spreading sequences Sj (t), j = 0,1,..., M−1, t = 0,1,. , L−1. Here, M and L are determined so as to satisfy w <M ≦ N and w <L ≦ N.

拡散系列Ｓｊ（ｔ）は、ゼロ自己平均、ゼロ相互相関、定数の自己相関を有する±１からなる列である。例えば、［数２］に示すように、±１で構成される直交変換であるウォルシュ変換の変換列を用いることができる。［数２］はＭ＝８，Ｌ＝８の場合のウォルシュ変換の変換列である。

The spreading sequence Sj (t) is a sequence of ± 1 having zero self-average, zero cross-correlation, and constant autocorrelation. For example, as shown in [Equation 2], it is possible to use a transform sequence of Walsh transform that is orthogonal transform composed of ± 1. [Equation 2] is a conversion sequence of Walsh transform when M = 8 and L = 8.

この拡散系列Ｓｊ（ｔ）を用いて電子透かし情報ｗを拡散した電子透かし列Ｗ（ｔ）は［数３］のように表される。ここでαは電子透かしの強さを調節するパラメータである。

An electronic watermark sequence W (t) obtained by diffusing the digital watermark information w using the spread sequence Sj (t) is expressed as [Equation 3]. Here, α is a parameter for adjusting the strength of the digital watermark.

ここで埋め込み対象画像Ｉｎ（ｘ）の離散フーリエ成分Ｆ＿ｉｎ（ｕ）に電子透かし情報を埋め込む。離散フーリエ成分Ｆ＿ｉｎ（ｕ）は［数４］のように表される。

Here, the digital watermark information is embedded in the discrete Fourier component F_in (u) of the embedding target image In (x). The discrete Fourier component F_in (u) is expressed as [Equation 4].

０≦ｕ≦Ｎ／２−１からＬ個をランダムに選択し、これをｕｔとする。ただし、ｔ＝０，１，・・・Ｌ−１である。これを用いて［数５］により電子透かしの埋め込みを行う。

L pieces are randomly selected from 0 ≦ u ≦ N / 2-1 and set as ut. However, t = 0, 1,... L-1. Using this, the digital watermark is embedded by [Equation 5].

［数５］によって得られるＦ’＿ｉｎ（ｕ）の逆離散フーリエ変換により、［数６］に示すような電子透かし入りの画像データＩｎ’（ｘ）が得られる。

Image data In ′ (x) with a digital watermark as shown in [Formula 6] is obtained by inverse discrete Fourier transform of F′_in (u) obtained by [Formula 5].

次に、上記のようにして埋め込まれた電子透かし情報の検出方法について説明する。電子透かし情報が検証される対象画像をＩｎ’（ｘ）とする。この離散フーリエ成分Ｆ’＿ｉｎ（ｕ）は［数７］のように表される。

Next, a method for detecting the digital watermark information embedded as described above will be described. The target image whose digital watermark information is verified is assumed to be In ′ (x). The discrete Fourier component F′_in (u) is expressed as [Equation 7].

電子透かし情報の埋め込みにおいて用いた拡散系列である、［数１］の条件を満たす±１からなるＭ個の長さＬの拡散系列Ｓｊ（ｔ），ｊ＝０，１，・・・，Ｍ−１，ｔ＝０，１，・・・，Ｌ−１を生成する。次に、電子透かし情報の埋め込みにおいて０≦ｕ≦Ｎ／２−１からＬ個を選択したｕｔ，ｔ＝０，１，・・・Ｌ−１を用いて、Ｆ’＿ｉｎ（ｕｔ）からその平均成分を取り除く。すなわち、Ｆ０をＦ’＿ｉｎ（ｕｔ），ｔ＝０，１，・・・Ｌ−１の平均値として、［数８］を計算する。

.., M spreading sequences Sj (t), j = 0, 1,..., M having a length of ± 1 satisfying the condition of [Equation 1]. −1, t = 0, 1,..., L−1 are generated. Next, when embedding digital watermark information, L = ut, t = 0, 1,..., L−1 selected from 0 ≦ u ≦ N / 2-1 are used, and F′_in (ut) Remove the average component. That is, [Equation 8] is calculated by setting F0 as an average value of F′_in (ut), t = 0, 1,... L−1.

このＦ’’＿ｉｎ（ｕｔ）と拡散系列Ｓｊ（ｔ）とを用いて［数９］の相関列Ｂ（ｊ）を計算し、電子透かしの検出を行う。

Using this F ″ _in (ut) and the spreading sequence Sj (t), the correlation sequence B (j) of [Equation 9] is calculated, and the digital watermark is detected.

［数９］の相関列Ｂ（ｊ），ｊ＝０，１，・・・，Ｍ−１が最大値を取るｊの値が検出された電子透かし情報ｗである。なお、［数９］の相関列は正規化されているが、分母の項はパラメータｊと関係無く定数であるため、実際電子透かし検出に用いる相関列は［数１０］により計算される。

This is the electronic watermark information w in which the value of j where the correlation string B (j), j = 0, 1,... Although the correlation sequence of [Equation 9] is normalized, the denominator term is a constant regardless of the parameter j, and thus the correlation sequence used for actual digital watermark detection is calculated by [Equation 10].

ここで、上記で説明した相関型の電子透かしの検出結果の例を示す。図２の上段のグラフは、電子透かしが埋め込まれた正規品をスキャンし、上記のようにして相関列Ｂ（ｊ）を計算した結果の一例を示す。グラフの横軸はｊの値、縦軸はＢ（ｊ）の値を示し、前述のようにＢ（ｊ）が最大値を取るｊの値が検出された電子透かしである。
図２の中段のグラフは、正規品をスキャンして印刷したコピー品について、これをスキャンして上記のようにして相関列Ｂ（ｊ）を計算した結果の例である。Ｂ（ｊ）が最大値をとるｊの値は正しく検出されたものの、Ｂ（ｊ）の最大値が弱くなっている。
図２の下段のグラフは、コピー品のコピー品、すなわち、コピー品をスキャンして印刷したものについて、これをスキャンして上記のようにして相関列Ｂ（ｊ）を計算した結果の例である。この場合は、Ｂ（ｊ）が最大値をとるｊの値は正しく検出されなかった。
以上の例から分かるように、ここで用いる相関型の電子透かしは正規品とコピー品において検出される相関列Ｂ（ｊ）の最大値あるいは最大値をとるｊの値が異なる。相関型の電子透かしのこのような特性に基づいて、以下、真贋チェックにおいて用いる信頼度及び判別しきい値を求める。
以上、離散フーリエ変換の成分への電子透かしの埋め込みおよび検出を例としてあげたが、離散フーリエ変換やその他の変換を利用せず、直接画像データに相関型の電子透かしを埋め込み、または、直接画像データから相関型の電子透かしを検出するものも含まれる。あるいは、その他変換を利用した相関型の電子透かし埋め込みと検出の手法も含まれる。

Here, an example of the detection result of the correlation type digital watermark described above is shown. The upper graph in FIG. 2 shows an example of a result obtained by scanning a genuine product in which a digital watermark is embedded and calculating the correlation sequence B (j) as described above. The horizontal axis of the graph indicates the value of j, the vertical axis indicates the value of B (j), and the electronic watermark in which the value of j where B (j) takes the maximum value as described above is detected.
The middle graph in FIG. 2 is an example of the result of calculating the correlation sequence B (j) as described above for a copy product obtained by scanning a regular product and printing it. Although the value of j at which B (j) has the maximum value is correctly detected, the maximum value of B (j) is weak.
The lower graph of FIG. 2 shows an example of the result of calculating the correlation sequence B (j) as described above by scanning a copy product of a copy product, that is, a copy product scanned and printed. is there. In this case, the value of j where B (j) has the maximum value was not correctly detected.
As can be seen from the above examples, the correlation type digital watermark used here differs in the maximum value of the correlation string B (j) detected in the regular product and the copy product or the value of j that takes the maximum value. Based on such characteristics of the correlation type digital watermark, the reliability and the discrimination threshold used in the authenticity check are obtained below.
In the above, embedding and detection of a digital watermark in a component of the discrete Fourier transform has been described as an example. However, without using a discrete Fourier transform or other transformation, a correlation type digital watermark is directly embedded in image data, or a direct image is obtained. Also included are those that detect correlated digital watermarks from data. Alternatively, a correlation type digital watermark embedding and detection method using other conversion is also included.

  First, how to obtain the reliability will be described. For the sequence B (j), j = 0, 1,..., M−1 obtained by [Equation 10], the average and standard deviation are obtained and are set as μ and σ, respectively. Using this, the detection strength of the digital watermark is determined by [Equation 11]. That is, in [Expression 11], the detection intensity D is a value obtained by subtracting the average μ from the maximum value of the sequence B (j) and dividing the result by the standard deviation σ of the sequence.

次に、この検出強度Ｄを用いて、電子透かしの信頼度を［数１２］で定義する。

Next, the reliability of the digital watermark is defined by [Equation 12] using the detection intensity D.

［数１２］のΦ（ｘ）は［数１３］で定義される関数である。これは正規分布における０からｘまでの累積密度関数であり、図３はこの関数による値をグラフに表したものである。

Φ (x) in [Equation 12] is a function defined by [Equation 13]. This is a cumulative density function from 0 to x in a normal distribution, and FIG. 3 is a graph showing the value of this function.

［数１２］においてＤｒは、正規品のうち基準として定めたものについての、［数１１］による電子透かしの検出強度である。しかし、同一の印刷機により印刷された正規品であっても、電子透かしを検出した場合には検出強度にばらつきがある。これを考慮して、基準となる正規品を複数選択してこれらの検出強度を求め、その平均を計算してＤｒとしてもよい。

In [Equation 12], Dr is the detection strength of the digital watermark according to [Equation 11] for a genuine product determined as a reference. However, even if it is a regular product printed by the same printer, the detection intensity varies when the digital watermark is detected. In consideration of this, it is possible to select a plurality of reference regular products, obtain the detected intensities thereof, calculate the average thereof, and obtain Dr.

  Next, how to determine the discrimination threshold will be described. This discrimination threshold is obtained by using a genuine product for the pair of the printing press P and the capture device S. Here, the printing press P is a printing press on which a regular product is printed, and the capture device S is a device that scans the regular product when obtaining the reliability of the digital watermark and the determination threshold value. First, one regular product A and N test regular products Bi, i = 1, 2,..., N are selected from regular products. Next, the detection intensity Dr of the reference regular product A is obtained by [Equation 11], and the reliability Ri, i = 1, 2,... For N test regular products by [Equation 12] using this Dr. ..N is obtained. Next, the average Av_R and standard deviation σ_R of Ri, i = 1, 2,..., N are obtained, and the discrimination threshold T_ps is obtained from [Equation 14].

［数１４］においてλは判別誤差を調整するパラメータであり、偽造品判定率を上げるには、λを１．０より小さく設定する。ただし、この場合は正規品拒否率も上げることになる。逆に、偽造品判定率を下げるには、λを１．０より大きく設定する。標準では、λ＝１．０とする。Ｔ＿ｐｓは印刷された画像の種類毎に判別しきい値を定めると、より判別精度が高められる。
なお、上記で基準となる正規品Ａを１つ選択し、基準となる正規品の検出強度Ｄｒを求めたが、上記と同様に検出強度のばらつきを考慮して、基準となる正規品Ａを複数選択してこれらの検出強度を求め、その平均を計算してＤｒとしてもよい。

In [Equation 14], λ is a parameter for adjusting the discrimination error. In order to increase the counterfeit product judgment rate, λ is set to be smaller than 1.0. However, in this case, the genuine product refusal rate is also increased. Conversely, to lower the counterfeit product determination rate, λ is set to be larger than 1.0. In the standard, λ = 1.0. The determination accuracy of T_ps can be further improved by setting a determination threshold value for each type of printed image.
In addition, one normal product A as a reference was selected and the detection strength Dr of the reference regular product was obtained. In the same manner as described above, taking into account variations in detection strength, Dr. may be obtained by calculating a plurality of selected detection intensities and calculating an average thereof.

  Using the discrimination threshold value T_ps determined for the pair of the printing press P and the capture device S as described above, the authenticity of the printed matter is determined. That is, when the reliability R of the printed material to be determined is larger than the determination threshold value T_ps, it is determined as a regular product, and when it is not, it is determined as a copy product. Since the determination threshold value T_ps is obtained by determining a pair of the printing press P and the capture device S, the image data of the printed material to be determined is captured using the reading device S when performing the authenticity check. The printer P and the reading device S are preferably the same device, that is, the same serial number, but the same determination threshold value may be used if the model is the same. Therefore, even if the print data is the same, if the model of the printing press or the model of the reading device is different, it is necessary to individually determine the discrimination threshold for the pair.

  Based on the above, a method for checking the authenticity of a printed matter will be described with reference to FIG. FIG. 1 is a diagram showing the overall flow of a printed matter authenticity check in this embodiment. This overall flow is composed of a block 10 for printing a printed material for distribution, a block 20 for determining a discrimination threshold used in authenticity checking based on a genuine product, and a block 30 for performing authenticity checking for the distributed material. The

  First, in step S11 of block 10, printing by the printing press P is performed. In this method, a correlation type digital watermark is embedded in print data, and printing is performed by using the print data using a printing medium such as paper and plastic, ink, and the like by using the print data. The printed printed matter 40 with the electronic watermark check function is, for example, a card with a photograph or an image, a magazine, or a package. When such a legitimate printed product is distributed, a counterfeit product may be created, for example, by printing it as image data using a scanner, digital camera, etc., or copying it using a copier. . Here, the counterfeit product does not include a product printed using the original print data used in step S11 when it is leaked.

  In order to determine whether the printed material distributed as described above is a genuine product or a counterfeit product, a determination threshold value used for the determination is obtained in block 20. First, a regular product as a reference is selected (step S21) and a test regular product is selected (step S22), and these images are captured by the capture device S (step S23). Based on the detection intensity obtained by detecting the watermark, the discrimination threshold T_ps is obtained as described above (step S24). In block 30, an image is captured by the capture device S for the printed matter to be checked using the determination threshold value (step S 31), and a determination based on the determination threshold value T_ps is performed. Here, as the discrimination threshold T_ps, a value corresponding to a pair of the printing press P and the capture device S is used.

The flow in the block 20 and the block 30 will be described in detail with reference to FIGS. 4 and 5, respectively.
FIG. 4 is a flowchart for calculating values used for checking the authenticity of a printed material. First, the regular product A and the test regular product Bi, i = 1, 2,..., N are selected from the printed matter 40 with the electronic watermark check function printed by the printing press P (step S201). . Next, these are digitized by the capture device S and captured as image data (step S202). Next, a digital watermark is detected from the captured image data, and the detection strength Dr of the regular product A serving as a reference and the detection strength Di of the test regular product Bi, i = 1, 2,. .., N is calculated, and based on this, reliability Ri, i = 1, 2,..., N is calculated according to [Equation 12] (step S203). Next, an average Av_R and standard deviation σ_R of Ri are calculated (step S204). Further, from these, the determination threshold value T_ps is obtained by [Equation 14].

FIG. 5 is a flowchart for checking the authenticity of the printed material. Here, it is determined whether the printed material to be checked is a printed material 40 with a digital watermark check function or a copy product. In the case of a copy product, the print product input in step S301 is a copy product printed by scanning the print product 40 with the electronic watermark check function.
First, the printed material to be determined is digitized by the capture device S and captured as image data (step S301). Next, digital watermark detection and detection intensity D are calculated from the captured image data (step S302). Next, it is determined whether the digital watermark has been correctly detected in step S302 (step S303). If the determination result is “NO”, it is a copy product. When the determination result is “YES”, the reliability R is calculated by [Equation 12] using the detection intensity Dr of the regular product that is the reference calculated in step S203 of FIG. 4 (step S304). Next, it is determined whether the detected reliability R is greater than the determination threshold value T_ps (step S305). If the determination result is “NO”, it is a copy product. If the determination result is “YES”, it is a genuine product.

  FIG. 6 shows the result of calculating the reliability R of the digital watermark detected from the genuine product, the copy product 1 and the copy product 2 for nine different images. Here, the authenticity of the genuine product is selected as a reference regular product and a test genuine product, the reliability and the discrimination threshold are calculated, and then the digital watermark is detected for another genuine product. It is a calculated value. Even regular products printed by the same printing press P vary depending on the image, and some of them are smaller than 1.0. The meanings of the copy product 1 and the copy product 2 are as already described in the explanation of the legend of FIG. The dotted line represents the discrimination threshold T_ps. The reliability of the copy product 1 and the copy product 2 is lower than this.

The authenticity check may be performed using a computer or a dedicated device having a computer inside. That is, using the computer or a dedicated device having a computer inside, processing for obtaining a discrimination threshold for the image data captured in step S202 by steps S203, S204, and [Equation 14], that is, a capture device Step S302, Step S303, Step S302 are performed on the image data captured in Step S301 by performing a process for obtaining a discrimination threshold based on the detected intensity of the correlation type digital watermark detected from the genuine image data captured in Step S301. The process for obtaining the reliability in S304, that is, the process for obtaining the reliability based on the detected intensity of the correlation type digital watermark detected from the image data of the print product to be checked for authenticity captured by the capture device may be performed.
The process of these operations is stored in a computer-readable recording medium in the form of a program, and the above processing is performed by the computer reading and executing this program. Here, the computer includes an OS and hardware such as peripheral devices.

  In addition to ROM, “computer-readable recording medium” refers to a storage device such as a magnetic disk, a magneto-optical disk, a portable medium such as a CD-ROM or a DVD-ROM, or a hard disk built in a computer. Say. Further, the “computer-readable recording medium” refers to a volatile memory (RAM) in a computer or a system that becomes a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. In addition, those holding a program for a certain period of time are also included.

Further, the program may be transmitted from a computer storing the program in a storage device or the like to another computer via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line.
The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer, what is called a difference file (difference program) may be sufficient.

  The present invention is used for authenticity checking of printed matter printed based on print data.

It is a figure which shows the whole flow of the authenticity check of the printed matter in this embodiment. It is a graph which shows the correlation value at the time of correlation type | mold digital watermark detection. It is a graph of the cumulative density distribution used for the definition of the detection reliability of a digital watermark. It is a flowchart which calculates the value used for the authenticity check of printed matter. It is a flowchart of the authenticity check of printed matter. It is a graph which shows the example of an authenticity check result. It is a graph which shows the example of the number of electronic watermark detection blocks. It is a figure which shows the example of the number of electronic watermark detection blocks.

Explanation of symbols

10, 20, 30: Block for classifying the entire flow 40: Printed matter with digital watermark check function

Claims (6)

In a method for checking the authenticity of a printed material for determining a genuine product printed with print data in which a correlation type digital watermark is embedded and a copy product forged based on the genuine product,
A first step of capturing image data from the regular product by a capture device and obtaining a discrimination threshold based on the detected intensity of the digital watermark detected from the image data;
A second step of acquiring image data from a printed matter to be checked for authenticity by the capturing device, and obtaining a reliability based on a detection strength of a digital watermark detected from the image data;
A third step of checking the authenticity of the printed matter by comparing the discrimination threshold and the reliability;
A method for checking the authenticity of printed matter having   In the first step, a reference genuine product and one or a plurality of test regular products are selected, and the detection strength of the digital watermark detected from the reference regular product and the digital watermark detected from the test genuine product are selected. 2. The method for checking the authenticity of a printed matter according to claim 1, wherein a reliability is obtained based on a difference from the detected intensity, and a discrimination threshold is obtained based on an average and standard deviation of the reliability.   The detection strength of the digital watermark detected from the regular product as the reference is an average of the detection strengths of the digital watermarks detected by selecting a plurality of regular products as the reference. How to check the authenticity of printed matter.   The reliability in the second process is obtained based on a difference between a detection strength of a digital watermark detected from a regular product that is a reference and a detection strength of a digital watermark detected from the printed material to be checked for authenticity. The method for checking the authenticity of a printed matter according to any one of claims 1 to 3. Means for determining a discrimination threshold based on the detected intensity of a correlation type digital watermark detected from genuine image data captured by a capture device;
Means for determining the reliability based on the detected intensity of the correlation type digital watermark detected from the image data of the printed matter to be checked for authenticity captured by the capture device;
A device for checking the authenticity of printed matter. Processing for obtaining a discrimination threshold based on the detected intensity of the correlation type digital watermark detected from the genuine image data captured by the capture device;
Processing for obtaining reliability based on the detected intensity of the correlation type digital watermark detected from the image data of the printed matter to be checked for authenticity captured by the capturing device;
A program that causes a computer to execute.

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