KR100403204B1 - Watermark embedding and extracting method for binary text and apparatus thereof - Google Patents

Abstract

The present invention relates to a watermark insertion and detection method and apparatus for tracing a document leakage path while protecting a copyright of a document by converting a document into a binarized image and inserting a watermark in the binarized document image.

When the document is processed offline, the document is converted to a binary image, and then the line processing unit is used to detect only the lines on which the letters are written, and to change the watermark by shifting the detected lines or converting them into a certain waveform. Insert it. At the time of detection, the watermark is detected by using a line-by-line processing device again to detect a line on which letters are written, and subtract the original document image from the watermarked document image to find the difference.

When the document is processed online, after converting the document into a binary image, the character unit is used to detect an area in which the letter is written as an area of one character unit, and to detect a value of '0' of the detected character area. The watermark is inserted by making the result of the modulo-2 operation of the number of pixels having the same value as the predetermined watermark. At the time of detection, the area in which the letters are written is detected as one letter unit area by using the letter unit processing device, and the watermark is detected by counting the number of pixels having a value of '0' in the detected letter area.

As described above, according to the present invention, watermarks can be inserted and detected both on and off-line for a document, increase the amount of watermark information to be inserted, and robust to partial editing of a document such as cutting on-line. It has the effect of providing a mark.

Description

WATERMARK EMBEDDING AND EXTRACTING METHOD FOR BINARY TEXT AND APPARATUS THEREOF}

The present invention relates to a watermark embedding and detection method for a binarized document, and more particularly, to converting a document into a binarized image and inserting a watermark into the document image. The present invention relates to a robust watermark embedding and detection method and apparatus thereof.

Recently, as digitization of binary texts such as various documents is progressed, various documents are generated by a document work program. Therefore, as the result is a digital file, it is difficult to find the source of the document, and illegal copying or forgery is easy. However, it is difficult to prevent forgery of the document itself, including tracking the source and leakage path of the document.

In particular, if a document written in a government office or a military agency is leaked on-line or off-line through a certain path, it is important to identify who leaked and who is the creator of the document.

The watermarking technique based on the present invention is known as a technique for protecting the copyright of digital files by adding and hiding certain information to digital data. Originally, watermark originated from the process of making papyrus (paper) in ancient times. Today, during the manufacturing of paper money, the paper is printed when the paper is wet, dried, and printed on both sides. It can also be used to enter. In other words, watermarking means any technical way of concealing and extracting a special form of watermark (ie information) in order to protect a series of copyrighted works.

In particular, a method of watermarking a document can be divided into a method of changing the position of the text and a method of changing the text, and a method of inserting a watermark in a visible manner may include a logo or a barcode.

There are two ways to change the position of the text: using line shifting of the text and word shifting. It is a method of placing a control line) or a fixed word (that is, a word group) and checking the presence or absence of a watermark based on this.

This method has a disadvantage in that the amount of information that can be inserted into the watermark is small by moving the fixed point up and down or left and right. In addition, there is a disadvantage that the amount of information (i.e., watermark) that can be inserted is further limited by excluding lines that do not meet the predetermined reference value.

One way to change text is to insert a watermark by applying masking on a block-by-block basis. However, since the document image is basically a binary image, it is composed of '0' and '1', so that some distortions appear as black dots or white dots. This is not only severe but also poor in terms of watermark detection performance.

The present invention is to solve the problems described above, an object of the present invention by using a watermarking technology to insert and detect a watermark in the document to track the leakage path of the document, to prevent the illegal copying of the document copyright holder Is to protect the copyright.

Another object of the present invention is to apply certain methods for document watermarking so that a watermark can be detected both on-line and on-line.

It is still another object of the present invention to provide a document watermarking technique which increases the amount of watermark information to be inserted and is robust against partial editing of a document such as online cutting.

1A is a block diagram schematically showing the configuration of a watermark embedding apparatus according to a first embodiment of the present invention.

1B is a block diagram schematically showing the configuration of a watermark detection apparatus according to the first embodiment of the present invention.

FIG. 2 (a) is a block diagram showing the configuration of the line processing apparatus of FIG. 1a, and FIG. 2 (b) is a graph showing an example of obtaining sum values of pixels through the horizontal projection apparatus of FIG. 2 (a). to be.

FIG. 3 is a diagram illustrating inserting a watermark by changing a line detected by the watermark insertion unit of FIG. 1A into a predetermined waveform.

4A is a block diagram schematically showing the configuration of a watermark embedding apparatus according to a second embodiment of the present invention.

4B is a block diagram schematically showing the configuration of the watermark detection apparatus according to the second embodiment of the present invention.

FIG. 5 (a) is a block diagram showing the structure of the letter unit processing apparatus of FIG. 4a, and FIG. 5 (b) is a graph showing an example in which the sum value of pixels is obtained through the vertical projection apparatus of FIG. 5 (a). to be.

6 is a diagram illustrating an example block arrangement of detected letters.

Explanation of symbols on the main parts of the drawings

100, 300: watermark inserting device 110, 310: binarization image converting device

120, 210: Line unit treatment device 122, 322: Horizontal projection device

124, 324: line detection device 130, 330: watermark insertion unit

140, 250: 1-D watermark generator 200, 400: watermark detector

220, 420: watermark extraction unit 230: subtractor

240, 430: correlation calculation unit 260: comparator

320, 410: character unit processing unit 326: vertical projection unit

328: Text detection device 340, 440: 2-D watermark generating device

In order to achieve the above object, the present invention provides a method of inserting a watermark into a document in order to track the leakage path of a printed and outgoing document and to protect the copyright of the document. Converting to a binarized image; (b) detecting only lines in which characters are written in the binarized document image; And (c) embedding a watermark in the detected line.

Here, in the step (c), it is preferable to insert the watermark by shifting the detected line to the left or right, or by modifying the detected line to form a waveform of a certain shape.

According to another aspect of the present invention, there is provided a method of detecting a watermark from a watermarked binarized document image, the method comprising: (a) detecting a line on which a character is written in the watermarked document image; And extracting the watermark by subtracting the original document image from the watermarked document image and obtaining the difference.

In order to achieve another object of the present invention, the present invention provides a method for inserting a watermark in a document in order to track the leak path of the document leaked online and to protect the copyright of the document, (a) a document creation program Converting the document created in the binary image into a binarized image; (b) detecting an area in which a letter is written in the document image as an area of one letter unit; And (c) inserting a watermark by causing a predetermined operation result of the number of pixels having a '0' value of the text area to be equal to a predetermined watermark.

Here, in step (c), the pixel value of the detected text area is compared with the pixel value of a predetermined watermark through a modulo-2 operation, and then the number of pixels having a '0' value of the detected text area is compared. It is preferable that the watermark is inserted by making the result of the modulo-2 operation equal to the number of pixels having a '0' value of the predetermined watermark.

In order to achieve another object of the present invention, the present invention provides a method for detecting a watermark from a watermarked binarized document image, the method comprising the steps of: Detecting; And (b) extracting the watermark by counting the number of pixels having a value of '0' in the detected area.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, a watermark embedding and detecting apparatus according to a first embodiment of the present invention will be described with reference to FIGS. 1A to 3. The first embodiment of the present invention is a case in which a document is processed off-line, and the off-line processing of a document means a case in which a document created by a document creating program is outputted by a printer and leaked, which will be described in detail below. Let's do it.

1A is a block diagram schematically showing the configuration of the watermark embedding apparatus 100 according to the first embodiment of the present invention.

Referring to FIG. 1A, the watermark embedding apparatus 100 of the first embodiment of the present invention is a binarized image converting apparatus 110 for converting a document created by a document creating program into a binarized image (i.e., an image), a binarized image. The unit of line processing unit 120, the 1-D watermark generating unit 140, and the detected lines to extract the index of the line on which the letter is written, and the position of the letter according to the watermark And a watermark inserting unit 130 for inserting the watermark by changing accordingly.

First, a document (for example, a word file or a Hangul file, etc.) created by a document creation program is converted into a binarized image by the binarization image converting apparatus 110. Such conversion into a binarized image is similar to that of converting a document into a PDF file, for example, by the VPD (Virtual Print Driver) in the present invention.

The VPD is a specific print driver that performs document imaging and watermark insertion. When the print command of the created document is executed, the VPD images each document page by page. In addition, there is an option of online / offline to execute such a print command. In the first embodiment of the present invention, a binary image is selected through the following line-by-line processing and watermark embedding process by selecting the offline option. It will be output by the printer.

The document image binarized by selecting the offline option is processed in the line processing unit 120, and the configuration and processing of the line processing unit 120 will be described with reference to FIGS. 2 (a) and 2 (b). Will be explained.

FIG. 2A is a block diagram showing the configuration of the line processing apparatus 120 of FIG. 1A.

Referring to Fig. 2A, the document image input to the horizontal projection apparatus 122 is projected horizontally, and the pixel values are summed. The black text in the document is displayed as '0' and the white background is displayed as '1'. Thus, if no letters are written on the line, the sum is equal to the width of the document. If the sum is not equal to the width of the document, it means that any content has a letter or symbol on the line.

FIG. 2B is a graph showing an example in which the sum value of pixels is obtained through the horizontal projection apparatus 122 of FIG.

Referring to FIG. 2 (b), in the sum value of the pixels through horizontal projection, the sum value of the line on which the letter is written does not become the width value of the document, and the sum value of the line without the letter is on the sum value. You can see that it is equal to the width of this document.

Referring again to FIG. 2 (a), on the basis of the sum value obtained by the horizontal projection apparatus 122, the index of the line on which the letter is written is output from the line detection apparatus 124.

Referring again to FIG. 1A, the detected character is generated according to a watermark (consisting of '1' and '0') generated by the 1-D watermark generator 140 (that is, the one-dimensional watermark generator). The process of inserting a watermark by shifting a line marked with (or shifting to the left in this embodiment) or dividing a line into two waveforms (sine wave or triangle wave) is performed. It is performed in the insert 130.

A process of inserting a watermark by changing a line into a waveform in the watermark inserting unit 130 will be described with reference to FIG. 3. 3 is a diagram illustrating inserting a watermark by changing a line detected by the watermark inserting unit 130 of FIG.

Referring to the line on which the letters shown in Fig. 3 (a) are written, it is shown that the letters gradually increase from the beginning of the line to the middle of the line, and the characters gradually descend from the middle of the line to the end of the line. The watermark value of this line may be, for example, (1,1). That is, when the watermark value is '1', the slope of the line may be raised or lowered. When the watermark value is '0', the slope of the line may be expressed as zero. Accordingly, the watermark value of the line shown in FIG. 3B may be represented by (1,0), and thus the watermark value may be inserted in the form of a predetermined waveform for each line. Also, as shown in Figs. 3C and 3D, the watermark value may be inserted in the form of a waveform such as a sine wave.

However, it is desirable to avoid abrupt line shape changes for continuity of document lines. That is, when the watermark is '1' and the slope is set to 45 degrees, when the next phrase is '1' again, a discontinuity is generated and the watermark becomes conspicuous. To prevent this, the waveform is adjusted in consideration of the watermark values before and after the current watermark value.

As a result, a watermarked document is created, and the process of inserting the watermark processed line by line for offline processing is completed. In the present invention, the entire process of embedding such a watermark is performed by, for example, a VPD, thereby eliminating the need to install a watermarking program on the user's side of the document and automatically controlling the printer at the printer side. .

Next, the watermark detection apparatus 200 according to the first embodiment of the present invention will be described with reference to FIG. 1B.

1B is a block diagram schematically showing the configuration of the watermark detection apparatus 200 according to the first embodiment of the present invention.

Referring to FIG. 1B, the watermark detection apparatus 200 according to the first exemplary embodiment of the present invention includes a line unit processing apparatus 210 for extracting an index of a line on which a character is written from a binarized image, and a watermarked document. A watermark extraction unit 220 for extracting watermarks from the watermarks, a correlation calculator 240 for obtaining a correlation between the extracted watermarks and the original watermarks, and a 1-D watermark generator 250 ), A subtractor 230 for obtaining a difference between the watermarked document and the original document, and a comparator 290 for comparing the printed watermarked document with the printed original document.

First, similarly to the watermark embedding process of FIG. 1A, the watermarked binarized image passes through the line processing unit 210. In addition, the watermarked document may be shifted to the left side in the watermark embedding process, for example. Therefore, when the subtractor 230 subtracts the original binarized image from the watermarked binarized image, the difference between the two documents appears.

If the difference between the position coordinates of the lines on which the characters detected by the line processing unit 210 are written is set to '1' and the portion without the difference is set to '0', the watermark is extracted as well. The user information on who created the document can be found by the watermark extracting unit 220, thereby enabling user authentication.

On the other hand, there is also a method for detecting a watermark by directly printing the watermarked document and the original document without using the above method. That is, when two documents printed on the comparator 260 are compared and checked, the difference between the lines (that is, the presence or absence of a shift) occurs in units of lines, so that it is possible to easily trace the author and the copyright of the document even with the naked eye.

In addition, if a watermark is inserted by dividing a line into two as shown in FIG. 3 and converting it into a waveform of a predetermined shape, watermark information can also be extracted as a waveform to track the leakage path and copyright of the document.

In addition, in order to enable detection of the watermark even when the binarization image is deformed and forged, the correlation calculation is performed, which will be described below.

That is, the correlation coefficient 240 determines the correlation coefficient between the watermark extracted from the watermark extractor 220 or the comparator 260 and the original watermark generated from the 1-D watermark generator 250. This is expressed by Equation 1 below.

From here, Is the inner product between the original watermark, Is the dot product between the extracted watermarks, Denotes a dot product between the original watermark and the extracted watermark, respectively. Corr also represents a correlation coefficient between the extracted watermark and the original watermark.

In addition, in the case of a document in which a part of the document is cut off or only partially, the presence or absence of a watermark may be determined through a fast fourier transform (FFT) to detect the watermark. Equation 2 below represents a watermark detection equation using an FFT.

From here, Is the original watermark Represents the extracted watermark, IFFT2 represents the 2D fast Fourier transform, FFT2 represents the 2D fast Fourier transform, and conj represents the conjugate complex number.

As a result, the watermark detection process of detecting the watermark from the watermarked document through the offline processing is completed.

Next, a watermark embedding and detecting apparatus according to a second embodiment of the present invention will be described with reference to FIGS. 4A to 6. In the second embodiment of the present invention, the document is processed online, and the on-line processing of the document means that the document created by the document creating program is leaked without being outputted by the printer. Of course, in the online processing of such a document, binarization imaging of the document is essential for the insertion of a watermark as in the present invention.

4A is a block diagram schematically showing the configuration of the watermark embedding apparatus 300 according to the second embodiment of the present invention.

Referring to FIG. 4A, the watermark embedding apparatus 300 according to the second embodiment of the present invention is a binarized image converting apparatus 310 for converting a document created by a document creating program into a binarized image, and the characters in the binarized image block by block. A character unit processing unit 320 for detecting a character, a 2-D watermark generating unit 340, and a watermark inserting unit 330 for inserting a watermark by counting the number of '0's in the detected block-shaped character area It includes.

First, similarly to the first embodiment, a document (for example, a word file or a Hangul file, etc.) created by the document creating program is converted into a binarized image by the binarization image converting apparatus 310. The second embodiment (i.e. online processing) is also made for example by the above-described VPD.

That is, when a print command of the created document is executed, each document is imaged on a page-by-page basis. Further, in the execution of such a print command, in the second embodiment of the present invention, among the options of online / offline, a document file is changed into a binary image by selecting an option of online. After that, the following character unit processing and watermark insertion are performed, and an image file is exported to a network or a diskette or the like.

In the second embodiment of the present invention (i.e., on-line processing), a document (i.e., a binarized image) to which a watermark is to be inserted is processed by the character unit processor 320, and the structure of the character unit processor 320 and its processing The process will be described with reference to FIGS. 5 (a) and 5 (b).

FIG. 5A is a block diagram showing the structure of the letter unit processing apparatus 320 of FIG. 4A.

Referring to FIG. 5 (a), similarly to the line processing apparatus 120 in FIG. 2 (a), the input binarized image first passes through the horizontal projection device 322 and the line detection device 324. As a result, the line on which the letter is written is detected.

Thereafter, the detected line is vertically projected on the vertical projection device 326 to separate the characters in units of actual letters from the detected lines. The black text in the line is displayed as '0' and the white background is displayed as '1'. Therefore, if no letter is written in the predetermined area of the detected line, the sum of the pixels in the area becomes equal to the height of the line. If the sum in any area is not equal to the height of the line, it means that the area of the line contains letters or symbols.

FIG. 5B is a graph showing an example in which the sum value of pixels is obtained through the vertical projection device 326 of FIG.

Referring to FIG. 5 (b), in the sum value of pixels through vertical projection, in the area of the line where the letter is written (that is, the letter area), the sum value is not equal to the height of the line, and the letter is written. In an area of the line that is not present (i.e. letter spacing), the sum is equal to the line height.

Referring again to Fig. 5A, based on the sum value obtained in the vertical projection device 326, the character area is detected by the character detection device 328.

In the detection of the character area in the character detection apparatus 328, the detected character area (i.e., the area where the character has passed through the horizontal projection and the vertical projection) is arranged in blocks as shown in FIG.

Referring again to FIG. 4A, the watermark inserting unit 330 counts the number of pixels corresponding to '0' in the area for each letter extracted in the shape of a block, and the 2-D watermark generator 340: That is, the watermark generated by the 2D watermark generator is compared with each other through modulo-2 operation.

This calculation process is represented by the following equation (3).

Where S is the sum of the pixels having a value of '0', C is the pixel value in the s column of the k rows, and l and m are the height and width of the character area, respectively. In addition, R means the result of the modulo-2 operation.

If the modulo-2 operation result of the number of '0' pixels of the extracted character area is different from the watermark, the watermark insertion unit 330 is adjusted by adjusting the character area to be the same as the watermark. ) Is inserted.

As a result, a watermarked document is created, and the process of inserting the watermark processed in units of letters for processing online ends.

By the way, when the watermark is inserted, if the dot is placed at an arbitrary position or the dot at the arbitrary position is removed, damage to the document is likely to be noticeable by the insertion of the watermark. Therefore, there is a need for a method of determining a position to insert a watermark. To determine where the watermark is inserted, change the area of a single letter into a one-dimensional array and select a random point.

Search left and right based on an arbitrary point and when the search results change the value from '0' to '1', change the point of '1' to '0' or the point of '0' to '1'. Change to insert the watermark. By doing so, it is possible to prevent the document from being damaged, such as having a prominent mark on the document due to the insertion of the watermark.

Next, the watermark detection apparatus 400 according to the second embodiment of the present invention will be described with reference to FIG. 4B.

4B is a block diagram schematically showing the configuration of the watermark detection apparatus 400 according to the second embodiment of the present invention.

Referring to FIG. 4B, the watermark detection apparatus 400 according to the second embodiment of the present invention may include a character unit processing unit 410 for detecting a character for each block of characters in a binary document image, and a watermarked document. A watermark extractor 420 for extracting watermarks from the watermarks, a 2-D watermark generator 440, and a correlation calculator 430 for obtaining a correlation between the extracted watermarks and the original watermarks; )

First, the watermarked binarized image processed online passes through the character unit processing unit 410, and the processing performed by the character unit processing unit 410 is performed by the character unit processing unit 320 in the watermark insertion process of the second embodiment. Is the same as the processing in.

After passing through the character unit processing unit 410, the number of pixels having a value of '0' in the extracted character area is counted, and if the result is modulo-2, the result is a watermark value and the watermark is extracted. The author of the document can be known, and the leak path of the document can be known.

The processing performed by the correlation calculator 430 is the same as the processing performed by the correlation calculator 240 in the first embodiment (see FIG. 1B).

Although the invention has been particularly shown and described with reference to the above embodiments, it has been used for the purpose of illustration and those of ordinary skill in the art to which the invention pertains have the spirit and scope of the invention as defined in the appended claims. Various modifications can be made without departing.

As described above, according to the present invention, after converting a document into a binarized image through a virtual print driver (VPD), a watermark is inserted and detected through line-by-line processing and character-based processing, thereby preventing the user from perceptually recognizing it. After modification, the copyright holder's information can be extracted from the watermarked binarized document image.

It converts a document into a binarized image (i.e., an image file) and then inserts a watermark in the binarized image and detects it simultaneously, either offline or online. Therefore, the leakage path of the document can be tracked regardless of whether it is on or offline.

In addition, the present invention has the effect of increasing the amount of watermark information to be inserted, and providing a robust document watermarking technique for partial editing of documents such as online cutting.

Claims (25)

A method of embedding a watermark in a document in order to track the leakage path of a printed and outgoing document and to protect the copyright of the document, (a) converting a document created by a document creation program into a binarized image; (b) detecting only lines in which letters are written in the binarized document image; And (c) embedding a watermark in the detected line. The method of claim 1, The step (c) is a step of inserting a watermark by shifting the detected line to the left or right, or by modifying the detected line to form a waveform of a certain shape. The method of claim 2, The waveform is a waveform of a sinusoidal wave or a triangle wave. The method according to any one of claims 1 to 3, (B) the step of projecting the document image horizontally and summing the pixel values of the line to determine the line on which the letter is written, and outputting the index value of the line on which the letter is written. A method for detecting a watermark from a watermarked binarized document image, (a) detecting a line in which letters are written in the watermarked document image; And and (b) extracting a watermark by subtracting the original document image from the watermarked document image and obtaining the difference. The method of claim 5, The step (a) is a step of projecting the watermarked document image horizontally by summing the pixel values of the line to determine the line on which the letter is written, and outputting the index value of the line on which the letter is written. The method according to claim 5 or 6, After step (b), (c) detecting the watermark by calculating a correlation between the extracted watermark and the original watermark. The method of claim 7, wherein The correlation Corr2 calculation in the step (c) is calculated by the following equation, From here, Is the original watermark Represents an extracted watermark, IFFT2 represents a two-dimensional inverse fast Fourier transform, FFT2 represents a two-dimensional fast Fourier transform, and conj represents a conjugate complex number. A method of embedding a watermark in a document to track the leakage path of a document leaked online and to protect the copyright of the document, (a) converting a document created by a document creation program into a binarized image; (b) detecting an area where letters are written in the document image as an area of one letter unit; And and (c) inserting a watermark by causing a predetermined operation result of the number of pixels having a value of '0' of the character area to be equal to a predetermined watermark. The method of claim 9, In step (b), (b1) detecting a line on which letters are written by horizontally projecting the document image and summing pixel values of the line; And (b2) vertically projecting the detected line to detect an area in which the letter is written on the line. The method according to claim 9 or 10, In the step (c), the pixel value of the detected text area is compared with the pixel value of a predetermined watermark through a modulo-2 operation, and then modulo of the number of pixels having a '0' value of the detected text area. Inserting a watermark by making the result of the −2 operation equal to the number of pixels having a '0' value of the predetermined watermark. The method according to claim 9 or 10, Inserting the watermark in step (c), After changing the character area into a one-dimensional array, select an arbitrary point, search left and right based on the arbitrary point, and when the value of a position changes from '0' to '1' as a result of the search, A method for inserting a watermark by changing a point to '0' or a point of '0' to '1'. The method according to claim 9 or 10, The method of claim 1, further comprising disposing a letter area detected as an area of one letter unit in a block. A method for detecting a watermark from a watermarked binarized document image, (a) detecting an area where letters are written in the watermarked document image as an area of one letter unit; And (b) extracting a watermark by counting the number of pixels having a value of '0' in the detected area. The method of claim 14, In step (a), (a1) detecting a line on which letters are written by horizontally projecting the watermarked document image and summing pixel values of the line; And (a2) vertically projecting the detected line to detect an area in which the letter is written on the line. The method according to claim 14 or 15, After step (b), (c) detecting the watermark by calculating a correlation between the extracted watermark and the original watermark. The method of claim 16, The correlation Corr2 calculation in the step (c) is calculated by the following equation, From here, Is the original watermark Represents an extracted watermark, IFFT2 represents a two-dimensional inverse fast Fourier transform, FFT2 represents a two-dimensional fast Fourier transform, and conj represents a conjugate complex number. An apparatus for embedding a watermark in a document in order to track the outflow path of a printed and outgoing document and to protect the copyright of the document, A binarized image conversion device for converting a document created by a document creation program into a binarized image; A line unit processing unit for detecting only a line on which a character is written in the binarized document image; And And a watermark inserting unit for inserting a watermark by shifting the detected line to the left or right or changing the detected line to form a predetermined waveform. Insertion device. A watermark detection apparatus for detecting a watermark from a watermarked binarized document image, A line unit processing unit for detecting lines in which letters are written in the watermarked document image; And And a watermark extracting unit for extracting a watermark by subtracting an original document image from the watermarked document image and obtaining a difference thereof. The method of claim 19, And a correlation calculator for detecting a watermark by calculating a correlation between the watermark extracted by the watermark extractor and the original watermark. The method of claim 18 or 19, The line processing unit, A horizontal projection device for horizontally projecting the document image; And And a line detection device for determining the line on which the letter is written and outputting the index value of the line on which the letter is written by summing the pixel values of the line according to the result of the horizontal projection. An apparatus for embedding a watermark in a document in order to track the leak path of the document leaked online and to protect the copyright of the document, A binarized image conversion device for converting a document created by a document creation program into a binarized image; A character unit processing unit for detecting a region where characters are written in the document image as an area of one character unit; And And a watermark inserting unit for inserting a watermark by making a result of a modulo-2 operation of the number of pixels having a value of '0' of the character area detected by the character unit processing unit equal to a predetermined watermark. Watermark inserting device. An apparatus for detecting a watermark from a watermarked binarized document image, A character unit processing unit for detecting an area where characters are written in the watermarked document image as an area of one character unit; And And a watermark extraction unit for extracting a watermark by counting the number of pixels having a value of '0' in the character area detected by the character unit processing apparatus. The method of claim 23, And a correlation calculator for detecting a watermark by calculating a correlation between the watermark extracted by the watermark extractor and the original watermark. The method of claim 22 or 23, The character unit processing apparatus, A horizontal projection device for horizontally projecting the document image; A line detection device for determining a line on which letters are written and detecting a line on which letters are written by summing pixel values of the lines according to the horizontal projection result; A vertical projection device for vertically projecting the detected lines; And And a character detecting device which detects an area in the unit of letters by determining an area in which the letters are written in the line according to the result of the vertical projection.