Cryptography – By modifying optical image
Reexamination Certificate
1997-10-24
2001-08-07
Swann, Tod (Department: 2132)
Cryptography
By modifying optical image
C380S205000, C713S152000, C713S176000, C386S349000, C386S349000
Reexamination Certificate
active
06272222
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of and apparatus for manipulating digital data works, particularly to provide, or embed within, such digital data works, data descriptive of the work, for example, the source of the work, its ownership and its availability for legal reproduction without infringement of copyright.
DESCRIPTION OF THE PRIOR ART
Systems based upon digital data are becoming universal and indispensable; digital data passing between computers; digital telecommunications; digital audio; digital cameras; and the convergence of many of these individual components into multi-media, are a selection of the technologies to which this invention relates. The data structures or formats that are used in these different technologies are well documented and will not be described in this specification. It will however be appreciated by the skilled implementer that sophisticated encoding and compression algorithms are commonly used in digital recording and transmission and that these techniques may involve the manipulation of raw digital data in order for that data to carry further information. However, the further information introduced in such known techniques provides data needed to understand or handle, for example, bytes of the raw data properly.
The present invention is not directed to manipulating small units of digital data to enable that data to carry information inherent to the proper comprehension of the digital data itself but instead to hiding within a digital data work information that is specifically descriptive of that particular digital data work. The term digital data work defines any sequence of digital data capable of constituting a work in which copyright might subsist or the unauthorised reproduction of which might constitute infringement of any copyright subsisting in the work or a larger work of which the work itself forms a part. Hence, for example, the digital data defining the output from scanning a 35 mm colour transparency would be a digital data work.
There is a pressing need to enable the ownership of a digital data work to be readily apparent from the work itself. This would allow the owner of the copyright in the work to prove more readily its ownership and thereby prevent further unlawful reproduction or negotiate a licence fee for use of the work. Also, it would enable a publisher of digital data works, for example a company that compiles multi-media CD-ROMS, to ensure that it is not unwittingly infringing copyright. Conventionally, this requires laborious and meticulous manual recording of the provenance of third party digital data works that are to be used. This is time consuming, expensive and not wholly reliable.
As a more specific example, consider a professional photographer who uses a digital camera to take a digital photograph. He may wish to place the data file which constitutes the digital data work (the digitised photograph) with a photograph library. When the photograph is subsequently used, the photographer will be paid a copyright licence fee. However, the ease with which the data file can be duplicated without any loss of information means that the further use of the image can be impossible to control. In practice, there is a high probability that the image could be published again without the phoptographer being alerted to the fact; the photographer then losses out on licence fees. The ease with which digital images can be cropped and modified compounds the problem.
Currently, it is possible to include a simple identifier in the header of the data file of a digital data work. The header could typically comprise a simple copyright notice. However, it is very easy to strip out this information, making this approach unreliable. Further, translating a file into a different format also results in this information being lost.
Reference may also be made to Komatsu et al “A proposal on digital watermark in document image communication and its application to realising a signature”: Electronics and Communications in Japan vol. 73, no.5, May 31, 1990 New York pages 22-33, XP 000159282. That paper discloses a technique for modifying images in such a way that the modified image carries hidden information. However, the modification is corrupted if the image is manipulated; like a conventional watermark, it is designed to be corrupted or absent if the image is corrupted. Hence, it is of little practical benefit since unauthorised users of images can readily destroy the coded information by performing quite ordinary image manipulations, such as cropping and small rotations (e.g. rotations of plus or minus 1 degree needed in order to accurately set the horizon in an image).
Reference may also be made to EP 0551016 to Canon K K, which discloses a system for manipulating the position of dots forming a photocopy. The relative positions of the dots code for particular information. There is no modification however of a digital data work as such.
The practical requirements for a working system capable of embedding copyright information into a digital work are demanding:
1. the system must be reasonably rapid and not memory intensive;
2. the modifications which code for the additional information must not be readily perceptible;
3. the modifications must be sufficiently robust to withstand the manipulations ordinarily applied to those data woks (e.g. in the case of digital images, cropping and small rotations as described above);
4. the modifications must not be readily detectable or removable by any unauthorised user;
5. the modifications must be reliably detectable without reference to the original data work.
These requirements are met by the present invention.
STATEMENT OF THE INVENTION
In accordance with the present invention, a method of manipulating a digital data work, made up of a number of data elements, to include additional data descriptive of that digital data work, comprises the steps of:
dividing the whole or part of the work into a pattern of constituent parts, each constituent part consisting of a set of data elements and each set of data elements having a measurable characteristic;
selecting a particular constituent part;
modifying some or all of the set of data elements of that particular constituent part according to a given set of rules such that the measurable characteristic of that set is different from the measurable characteristic of the corresponding unmodified set of data elements, or other sets in other constituent parts,
wherein the difference is detectable, even after the work has undergone alternations which are of at least one kind of the alterations ordinarily applied to such works, if the pattern of the constituent parts and the nature of the measurable characteristic are known, but is not otherwise readily detectable;
and wherein the modification codes for the additional data descriptive of that digital data work.
Hence, the essence of the invention is to superimpose a selected pattern, generated by a given set of rules, on sets of data elements of the work thereby to modify the sets. The pattern may be a repeated pattern, although this is not essential. The invention can be conceptualised in terms of noise: all digital information has a noise element. This should be imperceptible. The present invention can be though of as organising this noise into regular patterns. The patterns themselves can contain information.
Where the work is an image, then the modification is, in one embodiment, superimposed on all pixels of the image, with the possible exception of those areas where such a pattern would be readily discernible to the ordinary viewer. The pattern or template may, for example, be the rows of the image and the modification may be the addition of +1 to every pixel in selected rows and the addition of −1 to every pixel in other selected rows. This modification produces only a slight change in the values describing any given pixel; however, because the pattern is applied across much or indeed preferably all of the image, the total information imparted can be considerable. The presence
Callahan Paul E.
Swann Tod
Woodbridge Richard C.
Woodbridge & Associates P.C.
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