Digital Watermarking as a form of Copyright Protection
by Thomas Page, Information Technology Group, Cameron McKenna
What is Digital Watermarking?
Watermarking of paper has been used as a form of identifying and validating documents for hundreds of years. The most obvious example is banknotes where watermarks are used as an extra layer of protection from counterfeiting.
Recent technology has allowed the principle of watermarking to be extended to digital images, audio and video files. As with the paper version, digital watermarking adds information which is normally invisible or barely visible to the naked eye, but which can be detected in order to identify the authenticity or copyright owner of the image, video or sound. For some purposes, however, a visible mark may actually be a better deterrent than an invisible mark and these are often used, for example, by cable and satellite television channels, where the station logo is often permanently placed in one corner of the screen.
Why is Watermarking useful?
This decade has witnessed an explosion in the distribution of electronic digital publishing via media such as compact discs, cd-roms and the internet as well as the latest technologies of digital video discs (DVDs) and digital television. This mass of digital technology has made copying and distributing illegal copies of copyright protected material fast, easy and cheap.
In order to combat the potentially disastrous losses to their revenue streams, the major owners and distributors of copyright material, such as image libraries, music and film companies and on-line publishers, have sought ways to detect and prevent copyright infringement. Watermarking enables these owners or distributors to label material in order to make detection and proof of infringement easier as can be seen from the case study below.
It is already possible to use a "spider" or "web crawler" to trawl the internet searching for images which contain a particular embedded copyright notice0. These spiders use software similar to those used by internet search engines, in that they will search sites and follow links from that site to others in order to cover as many sites as possible checking the images used on each page for watermarks.
IBM and NEC have recently agreed a standard for watermarking DVDs which they claim will enable them to prevent illegal copying. They propose to insert chips into DVD video players and DVD drives which would detect watermarks in copyright material and prevent the content being copied, as well as preventing the play-back of illegal copies of the content. However, in order to promote the use of recordable drives, users would still be able to make a single copy for back-up purposes or to make a single copy of a television broadcast for later viewing as is currently allowed for standard video recorders.
In some cases, watermarking can also be used to identify the source of the infringing material. A company which licenses images on-line and enables customers to download licensed images, can insert a separate watermark for each download with information identifying the licensee. If an unauthorised use of an image is discovered, then the watermark can be checked to determine from which licensee it came. It may be that the pirate copy was copied from a legitimate publication, but it helps a rightholder prevent unauthorised dissemination.
Watermarking may also be useful as a form of validation or authentication, for example in identity cards to prevent forgery. The producer of the identity cards could place a watermark in the "mugshot". When authentication of a card is required, the photograph can be scanned for a watermark and any image lacking such a mark would be identified as a forgery.
Watermarking versus Encryption
The only way to prevent copying and unauthorised use of digital information altogether is to encrypt it. Encryption scrambles the data into an illegible form which can only be decrypted by the intended recipient with the proper "key". This means that the material is secure in transmission by reason of its illegibility. However, weaker forms of encryption can be cracked by someone with sufficient time and processing power and in some countries there are legal restrictions on the use of stronger, supposedly unbreakable forms of encryption. The US government, for example, classes strong encryption as a weapon and prohibits the export of any strong encryption software1.
Encryption, however, has little use in the digital publishing industry where images are meant to be displayed in a visible format, whether on a webpage, in a computer game or on a cd-rom. Watermarking leaves the original image unchanged to the naked eye. It is also a permanent method of protecting the image - once material has been decrypted it is free of all protection and can be reproduced without hindrance or indication of the source. Watermarked images can always be traced and detected2.
As a result of the restrictions on the use of strong encryption, watermarking technology could in fact replace encryption in some circumstances. Anyone who wants to exchange secrets could use watermarking software to place a hidden message inside an innocuous image, video or audio file. A group of experts at the Universities of Dresden and Hildesheim have recently demonstrated a system for transmitting hidden data alongside speech over an ISDN line. The advantage of this system over encryption is that no one would know that the hidden message is there and it makes all the restrictions on strong encryption irrelevant.
Embedding of Digital Watermarks
Digital watermarking works by subtly altering parts of the information which forms the digital description of the image. A computer is able to encode a standard copyright notice and add it to, for example, the information which describes the colour balance of the image. The addition of this information will subtly change the colour of the image whenever it is displayed or printed, but the changes will be so slight that they are undetectable to the human eye. However, a computer equipped with the relevant software "reader" will easily be able to identify the changes and decode the information to identify the copyright notice.
Case Study - Contact Images LimitedContact is a publishing company which produces source books, cd-roms and a website containing information about photographers, illustrators and designers along with copies of their portfolios as well as libraries of images available for licensing. These books and cd-roms are distributed free to image users such as magazine and newspaper publishers who can then arrange to license images for publication as and when they need them. In order to prevent exploitation of the images, Contact uses the SureSign software from Signum Technologies to digitally watermark their images. These watermarks are still detectable when printed onto paper and then scanned back in to a computer meaning that Contact is able to detect and trace unauthorised copies of their images, whether they have been copied from the cd-rom or scanned in from the book and whether they are published on the net or in a magazine. Contact Images Limited |
One of the main problems faced by the developers of watermarking software is that of image processing. Digital images, by their nature, are easy to process in a number of ways, whether by compression methods (especially so-called ÒlossyÓ compression methods such as JPEG) to make transmission quicker or by manipulation of the image, such as blurring, filtering, or cropping. Any such form of processing may damage or even remove that part of the image in which the copyright information is encoded. In order for the watermark to survive simple processing, it is necessary to include the copyright notice in all parts of the image in information which is unlikely to be materially altered. For this reason, the watermarks are usually embedded in the frequency rather than spatial domains of an image, or in the colour or luminance bands which contain the most significant information of an image3.
There are various watermarking software products on the market4 and these use different methods to encode the copyright information. Each different method has its advantages depending on the precise form of protection required. At the moment, it appears that no watermarking products are completely immune from the processing of images, but if watermarks can only be removed by such heavy processing that the image is substantially different from the original then it will remain an effective deterrent to copyright infringement.
There are also at least two software products5 which claim to be able to delete watermarks which have been embedded by any of the main watermarking products on the market. These are being distributed as testing tools to determine how secure each system is, but inevitably will also be used by copyright pirates to remove notices and avoid detection. In using these products, there may well be deterioration of image quality and this may be sufficient to deter their use for unauthorised copying of high-quality images.
European Legislation
In December 1997 a proposal for a European Parliament and Council Directive was published on the harmonisation of certain aspects of copyright and related rights in the Information Society6 (the "Proposed Directive"). The Proposed Directive seeks to harmonise intellectual property protection throughout the EU and takes account of the provisions of the WIPO Treaties7. One of the provisions of the WIPO Treaties is to prohibit the removal or altering of certain electronic rights management information which is attached to a copyright work8.
For the purposes of the Proposed Directive, Article 7(2) defines "rights management information" to include any "information provided by rightholders which identifies the work, ... the author or any other rightholder, or information about the terms and conditions of use of the work ... and any codes that represent such information". This definition is wide enough to cover the copyright information inserted as a watermark into an image, video or audio file.
The European Commission recognises that technical developments such as watermarking facilitate the distribution of copyright material9 as owners become more confident that they have sufficient safeguards against widespread piracy of their works. At the moment, owners may be reluctant to distribute their copyright works outside the UK when they are uncertain as to the legal protection they will receive in other countries. In order to aid this process of wider distribution, the Commission proposes in Article 7(1) of the Proposed Directive to follow the WIPO Treaties in prohibiting the removal or alteration of electronic rights-management information, and the distribution, broadcasting communication or publishing of any copyright material from which such information has been removed or altered.
The WIPO Treaties and the Proposed Directive also deal with the use of "effective technical measures designed to protect copyright"10. These "technical measures" include only restricted access measures such as encryption or scrambling of broadcast signals and do not include watermarking. The Proposed Directive goes one stage further with these technical measures and Article 6(1) requires member states to implement legal protection against the manufacture or distribution of devices or the provision of services which have no commercial use other than the circumvention of such technical measures. There are no similar provisions in respect of devices or services to remove watermarks. However, it has been questioned as to whether the prohibition of de-scramblers, decrypters and watermark removers is actually in the public interest. Writers of such software argue that their software plays an important role in aiding the development of ever more secure systems - they liken themselves to "ethical hackers" employed by large companies such as BT to test the robustness of their IT networks. By proving that encryption can be cracked or watermarks removed, the writers of such software prevent the suppliers of encryption and watermarking software from becoming complacent in their claims of security and robustness.
Data Protection
In the Proposed Directive, the Commission also acknowledges that technology incorporating rights management information may be used to process personal data about the use of the copyright work by individuals and to trace on-line behaviour11. They note that any such technology must incorporate privacy safeguards in order to comply with the Data Protection Directive12.
This directive is in the process of being implemented into UK law. At the time of writing, the Data Protection Bill has just completed the standing committee stage in the House of Lords and is to be implemented by the 24th October 1998. However, the technology of tracing on-line behaviour goes beyond that of current watermarking software and discussion of the Data Protection Bill is a whole separate article in itself.
Conclusion
Digital watermarking is likely to become standard technology in the image and audio distribution industries and the technology will be incorporated into industry-standard image manipulation software such as Adobe Photoshop.
In conjunction, member states of the EU are likely to have to implement legislation to protect the watermarks from removal or alteration. Similar provisions are also being considered in the US as a result of the WIPO Treaties.
Together, these developments will enable rightholders to enforce their intellectual property rights by seeking out and prosecuting copyright pirates. As with much internet law, there are jurisdictional problems, with infringement being rife in countries with the least protection, but the proposed harmonisation provisions will at least ensure that rightholders are able to exploit fully their works commercially in a large part of the world markets.
Thomas Page
Cameron McKenna
email: tlp@cmck.com
Footnotes
0 MarcSpider™ from Digimarc Corporation - for more information see www.digimarc.com/prod_fam.html
1 Research has shown that 40-bit encryption, the strongest form allowable for export from the US, can be cracked by a so called "hardware brute force attack" in 0.002 seconds on average by an organisation with a computer system costing $100m (e.g. a government). (Source: Applied Cryptography).
2 But note watermark removal software discussed below (note 6).
3 For more information on the technical methods of embedding watermarks see "Watermarking Digital Images for Copyright Protection" by J.J.K. O Ruanaidh, F.M.Boland and O.Sinnen at cuiwww.unige.ch/~oruanaid/eva_pap.html; "Digital Watermarking" by Hal Berghel and Lawrence O'Gorman at www.acm.org/~hlb/publications/dig_wtr/dig_watr.html; and "Digital watermarking is the best way to protect intellectual property from illicit copying" by Jian Zhao in Byte magazine at www.byte.com/art/9701/sec18/art1.htm
4 For example, JK_PGS from Swiss Federal Institute of Technology, Lausanne, Switzerland, (EPFL); Digimarc™ from Digimarc Corporation; and SureSign from Signum Technologies.
5 (1) StirMark from Markus G. Kuhn; and (2) UnZign (no author credited - see www.altern.org/watermark/)
6 See COM(97) 628 final.
7 The WIPO Treaties consist of the WIPO Copyright Treaty (WCT) and the WIPO Performances and Phonograms Treaty (WPPT) which were adopted by the Diplomatic Conference on Certain Copyright and Neighbouring Rights Questions on the 20th December 1996. The Conference was convened by the World Intellectual Property Organisation (WIPO) in Geneva.
8 See Article 11 WCT and Article 18 WPPT
9 See Proposal for a Copyright Directive (COM(97) 628 final), recital 33
10 Ibid, Article 6(2)
11 Ibid, paragraph III.A.1 of Chapter 3 of the Explanatory Memorandum.
12 European Parliament and Council Directive 95/46/EEC.