Definition:
A digital watermark is a digital signal or pattern inserted into a digital document such as text, graphics or multimedia, and carries information unique to the copyright owner, the creator of the document or the authorized consumer.
Introduction:
Digital watermarking is a technique which allows an individual to add hidden copyright notices or other verification messages to digital audio, video, or image signals and documents. Such hidden message is a group of bits describing information pertaining to the signal or to the author of the signal (name, place, etc.).
The technique takes its name from watermarking of paper or money as a security measure. Digital watermarking is not a form of steganography, in which data is hidden in the message without the end user's knowledge, although some watermarking techniques have the steganographic feature of not being perceivable by the human eye.
The enormous popularity of the World Wide Web in the early 1990's demonstrated the commercial potential of offering multimedia resources through the digital networks. Since commercial interests seek to use the digital networks to offer digital media for profit, they have a strong interest in protecting their ownership rights. Digital watermarking has been proposed as one way to accomplish this.
A digital watermark is a digital signal or pattern inserted into a digital image. Since this signal or pattern is present in each unaltered copy of the original image, the digital watermark may also serve as a digital signature for the copies. A given watermark may be unique to each copy (e.g., to identify the intended recipient), or be common to multiple copies (e.g., to identify the document source).
In either case, the watermarking of the document involves the transformation of the original into another form. This distinguishes digital watermarking from digital fingerprinting where the original file remains intact, but another file is created that "describes" the original file's content. As a simple example, the checksum field for a disk sector would be a fingerprint of the preceding block of data. Similarly, hash algorithms produce fingerprint files.
Difference between ``copy protection'' and ``copyright protection’’
Copy protection attempts to find ways, which limits the access to copyrighted material and/or inhibit the copy process itself. Examples of copy protection include encrypted digital TV broadcast, access controls to copyrighted software through the use of license servers and technical copy protection mechanisms on the media. A recent example is the copy protection mechanism on DVDs. However, copy protection is very difficult to achieve in open systems, as recent incidents (like the DVD hack - DeCss) show.
Copyright protection inserts copyright information into the digital object without the loss of quality. Whenever the copyright of a digital object is in question, this information is extracted to identify the rightful owner. It is also possible to encode the identity of the original buyer along with the identity of the copyright holder, which allows tracing of any unauthorized copies. The most prominent way of embedding information in multimedia data is the use of digital watermarking.
Whereas copy protection seems to be difficult to implement, copyright protection protocols based on watermarking and strong cryptography are likely to be feasible.
History:
The term "digital watermark" was first coined in 1992 by Andrew Tirkel and Charles Osborne, in their paper: A.Z.Tirkel, G.A. Rankin, R.M. Van Schyndel, W.J.Ho, N.R.A.Mee, C.F.Osborne. “Electronic Water Mark”. DICTA 93, Macquarie University. p.666-673.
The term used by Tirkel and Osborne was originally used in Japan-- from the Japanese-- "denshi sukashi" -- literally, an "electronic watermark".
Paul LevinsonFuture of the Information Revolution (1997), where he called for the use "smart patent numbers" (p. 202), or the embedding of electronic chips in every piece of technology, which would give an updated listing of all of its inventors.
Whereas a digital watermark can be a form of steganography, e.g., the digital watermark is hidden in plain view. Functionally, the term "digital watermark" is used to describe that which enables differentiation between copies of the "same" content in an imperceptible manner. Many watermarking systems take this a step further, hiding the data so that attempts at erasure results in degradation of the quality of the content.
The Purpose of Digital Water Marking:
Two types of digital watermarks may be distinguished, depending upon whether the watermark appears visible or invisible to the casual viewer. Visible watermarks are used in much the same way as their bond paper ancestors, where the opacity of paper is altered by physically stamping it with an identifying pattern. This is done to mark the paper manufacturer or paper type. One might view digitally watermarked documents and images as digitally "stamped"
Invisible watermarks, on the other hand, are potentially useful as a means of identifying the source, author, creator, owner, distributor or authorized consumer of a document or image. For this purpose, the objective is to permanently and unalterably mark the image so that the credit or assignment is beyond dispute. In the event of illicit usage, the watermark would facilitate the claim of ownership, the receipt of copyright revenues, or the success of prosecution.
Watermarking has also been proposed to trace images in the event of their illicit redistribution. Whereas past infringement with copyrighted documents was often limited by the unfeasibility of large-scale photocopying and distribution, modern digital networks make large-scale dissemination simple and inexpensive. Digital watermarking makes it possible to uniquely mark each image for every buyer. If that buyer then makes an illicit copy, the illicit duplication may be convincingly demonstrated.
Techniques for Water Marking:
Watermarking techniques tend to divide into two categories, text and image, according to the type of document to be watermarked. Techniques for images: Several different methods enable watermarking in the spatial domain. The simplest (too simple for many applications) is to just flip the lowest-order bit of chosen pixels in a gray scale or color image. This will work well only if the image will not be subject to any human or noisy modification.
A more robust watermark can be embedded in an image in the same way that a watermark is added to paper. Such techniques may superimpose a watermark symbol over an area of the picture and then add some fixed intensity value for the watermark to the varied pixel values of the image.
The resulting watermark may be visible or invisible depending upon the value (large or small, respectively) of the watermark intensity. One disadvantage of spatial domain watermarks is that picture cropping (a common operation of image editors) can be used to eliminate the watermark.
Spatial watermarking can also be applied using color separation. in this way, the watermark appears in only one of the color bands. This renders the watermark visibly subtle such that it is difficult to detect under regular viewing.
However, the watermark appears immediately when the colors are separated for printing or xerography. This renders the document useless to the printer unless the watermark can be removed from the color band. This approach is used commercially for journalists to inspect digital pictures from a photo-Stackhouse before buying un-watermarked versions.
Watermarking can be applied in the frequency domain (and other transform domains) by first applying a transform like the Fast Fourier Transform (FFT). In a similar manner to spatial domain watermarking, the values of chosen frequencies can be altered from the original. Since high frequencies will be lost by compression or scaling, the watermark signal is applied to lower frequencies, or better yet, applied adaptively to frequencies that contain important information of the original picture (feature-based schemes).
Since watermarks applied to the frequency domain will be dispersed over the entirety of the spatial image upon inverse transformation, this method is not as susceptible to defeat by cropping as the spatial technique. However, there is more of a tradeoff here between invisibility and decodability, since the watermark is in effect applied indiscriminately across the spatial image.
Watermarking can be applied to text images as well. Three proposed methods are: text line coding, word space coding, and character encoding. For text line coding, the text lines of a document page are shifted imperceptibly up or down. For a 40-line text page, for instance, this yields 2**40 possible codewords. For word-shift coding, the spacing between words in a line of justified text is altered
For character coding, a feature such as the endline at the top of a letter, "t" is imperceptibly extended. An advantage of these methods over those applied to picture images is that, by combining two or three of these to one document, two documents with different watermarks cannot be spatially registered to extract the watermark. Of course, the watermark can be defeated by retyping the text.
Briefly following Technologies in particular type of water marking.
1) Techniques for Texts
1.1) Line Coding: Change the spacing between lines.
1.2) Word-shift Coding: Change the spacing between words.
1.3) Character Encoding: Alter the shapes of characters.
2) Techniques for Images
2.1)Spatial Watermarking: Just change some of the values of the pixels in the lower bit plane; e.g., Change some of the bits from 1 to 0 or 0 to 1.
2.2)Frequency Domain Watermarking: First convert the image to the frequency domain and then apply the watermark in the low frequency regions.
3.3)Checksum Technique for images
•Watermark is formed from the 7 most significant bits of each pixel.
•Eight 7-bit segments (from eight different pixels) are concatenated and the final checksum is thus 56-bit.
•Locations of the pixels that are to contain one bit each of the checksum are randomly chosen.
•These pixel locations along with the checksum form the watermark, W.
•Last bit of each pixel is then changed to the corresponding checksum bit.
A digital watermark is a digital signal or pattern inserted into a digital document such as text, graphics or multimedia, and carries information unique to the copyright owner, the creator of the document or the authorized consumer.
Introduction:
Digital watermarking is a technique which allows an individual to add hidden copyright notices or other verification messages to digital audio, video, or image signals and documents. Such hidden message is a group of bits describing information pertaining to the signal or to the author of the signal (name, place, etc.).
The technique takes its name from watermarking of paper or money as a security measure. Digital watermarking is not a form of steganography, in which data is hidden in the message without the end user's knowledge, although some watermarking techniques have the steganographic feature of not being perceivable by the human eye.
The enormous popularity of the World Wide Web in the early 1990's demonstrated the commercial potential of offering multimedia resources through the digital networks. Since commercial interests seek to use the digital networks to offer digital media for profit, they have a strong interest in protecting their ownership rights. Digital watermarking has been proposed as one way to accomplish this.
A digital watermark is a digital signal or pattern inserted into a digital image. Since this signal or pattern is present in each unaltered copy of the original image, the digital watermark may also serve as a digital signature for the copies. A given watermark may be unique to each copy (e.g., to identify the intended recipient), or be common to multiple copies (e.g., to identify the document source).
In either case, the watermarking of the document involves the transformation of the original into another form. This distinguishes digital watermarking from digital fingerprinting where the original file remains intact, but another file is created that "describes" the original file's content. As a simple example, the checksum field for a disk sector would be a fingerprint of the preceding block of data. Similarly, hash algorithms produce fingerprint files.
Difference between ``copy protection'' and ``copyright protection’’
Copy protection attempts to find ways, which limits the access to copyrighted material and/or inhibit the copy process itself. Examples of copy protection include encrypted digital TV broadcast, access controls to copyrighted software through the use of license servers and technical copy protection mechanisms on the media. A recent example is the copy protection mechanism on DVDs. However, copy protection is very difficult to achieve in open systems, as recent incidents (like the DVD hack - DeCss) show.
Copyright protection inserts copyright information into the digital object without the loss of quality. Whenever the copyright of a digital object is in question, this information is extracted to identify the rightful owner. It is also possible to encode the identity of the original buyer along with the identity of the copyright holder, which allows tracing of any unauthorized copies. The most prominent way of embedding information in multimedia data is the use of digital watermarking.
Whereas copy protection seems to be difficult to implement, copyright protection protocols based on watermarking and strong cryptography are likely to be feasible.
History:
The term "digital watermark" was first coined in 1992 by Andrew Tirkel and Charles Osborne, in their paper: A.Z.Tirkel, G.A. Rankin, R.M. Van Schyndel, W.J.Ho, N.R.A.Mee, C.F.Osborne. “Electronic Water Mark”. DICTA 93, Macquarie University. p.666-673.
The term used by Tirkel and Osborne was originally used in Japan-- from the Japanese-- "denshi sukashi" -- literally, an "electronic watermark".
Paul LevinsonFuture of the Information Revolution (1997), where he called for the use "smart patent numbers" (p. 202), or the embedding of electronic chips in every piece of technology, which would give an updated listing of all of its inventors.
Whereas a digital watermark can be a form of steganography, e.g., the digital watermark is hidden in plain view. Functionally, the term "digital watermark" is used to describe that which enables differentiation between copies of the "same" content in an imperceptible manner. Many watermarking systems take this a step further, hiding the data so that attempts at erasure results in degradation of the quality of the content.
The Purpose of Digital Water Marking:
Two types of digital watermarks may be distinguished, depending upon whether the watermark appears visible or invisible to the casual viewer. Visible watermarks are used in much the same way as their bond paper ancestors, where the opacity of paper is altered by physically stamping it with an identifying pattern. This is done to mark the paper manufacturer or paper type. One might view digitally watermarked documents and images as digitally "stamped"
Invisible watermarks, on the other hand, are potentially useful as a means of identifying the source, author, creator, owner, distributor or authorized consumer of a document or image. For this purpose, the objective is to permanently and unalterably mark the image so that the credit or assignment is beyond dispute. In the event of illicit usage, the watermark would facilitate the claim of ownership, the receipt of copyright revenues, or the success of prosecution.
Watermarking has also been proposed to trace images in the event of their illicit redistribution. Whereas past infringement with copyrighted documents was often limited by the unfeasibility of large-scale photocopying and distribution, modern digital networks make large-scale dissemination simple and inexpensive. Digital watermarking makes it possible to uniquely mark each image for every buyer. If that buyer then makes an illicit copy, the illicit duplication may be convincingly demonstrated.
Techniques for Water Marking:
Watermarking techniques tend to divide into two categories, text and image, according to the type of document to be watermarked. Techniques for images: Several different methods enable watermarking in the spatial domain. The simplest (too simple for many applications) is to just flip the lowest-order bit of chosen pixels in a gray scale or color image. This will work well only if the image will not be subject to any human or noisy modification.
A more robust watermark can be embedded in an image in the same way that a watermark is added to paper. Such techniques may superimpose a watermark symbol over an area of the picture and then add some fixed intensity value for the watermark to the varied pixel values of the image.
The resulting watermark may be visible or invisible depending upon the value (large or small, respectively) of the watermark intensity. One disadvantage of spatial domain watermarks is that picture cropping (a common operation of image editors) can be used to eliminate the watermark.
Spatial watermarking can also be applied using color separation. in this way, the watermark appears in only one of the color bands. This renders the watermark visibly subtle such that it is difficult to detect under regular viewing.
However, the watermark appears immediately when the colors are separated for printing or xerography. This renders the document useless to the printer unless the watermark can be removed from the color band. This approach is used commercially for journalists to inspect digital pictures from a photo-Stackhouse before buying un-watermarked versions.
Watermarking can be applied in the frequency domain (and other transform domains) by first applying a transform like the Fast Fourier Transform (FFT). In a similar manner to spatial domain watermarking, the values of chosen frequencies can be altered from the original. Since high frequencies will be lost by compression or scaling, the watermark signal is applied to lower frequencies, or better yet, applied adaptively to frequencies that contain important information of the original picture (feature-based schemes).
Since watermarks applied to the frequency domain will be dispersed over the entirety of the spatial image upon inverse transformation, this method is not as susceptible to defeat by cropping as the spatial technique. However, there is more of a tradeoff here between invisibility and decodability, since the watermark is in effect applied indiscriminately across the spatial image.
Watermarking can be applied to text images as well. Three proposed methods are: text line coding, word space coding, and character encoding. For text line coding, the text lines of a document page are shifted imperceptibly up or down. For a 40-line text page, for instance, this yields 2**40 possible codewords. For word-shift coding, the spacing between words in a line of justified text is altered
For character coding, a feature such as the endline at the top of a letter, "t" is imperceptibly extended. An advantage of these methods over those applied to picture images is that, by combining two or three of these to one document, two documents with different watermarks cannot be spatially registered to extract the watermark. Of course, the watermark can be defeated by retyping the text.
Briefly following Technologies in particular type of water marking.
1) Techniques for Texts
1.1) Line Coding: Change the spacing between lines.
1.2) Word-shift Coding: Change the spacing between words.
1.3) Character Encoding: Alter the shapes of characters.
2) Techniques for Images
2.1)Spatial Watermarking: Just change some of the values of the pixels in the lower bit plane; e.g., Change some of the bits from 1 to 0 or 0 to 1.
2.2)Frequency Domain Watermarking: First convert the image to the frequency domain and then apply the watermark in the low frequency regions.
3.3)Checksum Technique for images
•Watermark is formed from the 7 most significant bits of each pixel.
•Eight 7-bit segments (from eight different pixels) are concatenated and the final checksum is thus 56-bit.
•Locations of the pixels that are to contain one bit each of the checksum are randomly chosen.
•These pixel locations along with the checksum form the watermark, W.
•Last bit of each pixel is then changed to the corresponding checksum bit.
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