Electronic marking and identification techniques to discourage document copying

Modern computer networks make it possible to distribute documents quickly and economically by electronic means rather than by conventional paper means. However, the widespread adoption of electronic distribution of copyrighted material is currently impeded by the ease of illicit copying and dissemination. The authors propose techniques that discourage illicit distribution by embedding each document with a unique codeword. The encoding techniques are indiscernible by readers, yet enable one to identify the sanctioned recipient of a document by examination of a recovered document. The authors propose three coding methods, describe one in detail, and present experimental results showing that their identification techniques are highly reliable, even after documents have been photocopied.>