Copyright protection for the electronic distribution of text documents

Each copy of a rest document can be made different in a nearly invisible may by repositioning or modifying the appearance of different elements of text, i.e., lines, words, or characters. A unique copy can be registered with its recipient, so that subsequent unauthorized copies that are retrieved can be traced back to the original ou nei. In this paper Mle describe and compare sever al mechanisms for marking documents and several other mechanisms for decoding the mal ks after documents have been subjected to common types of distortion. The marks are intended to protect documents of limited value that are owned by individuals who would rather possess a legal than an illegal copy if they can be distinguished. We will describe attacks that remove the marks and countermeasures to those attacks. An architecture is described for distributing a large number of copies without burdening the publisher with creating and transmitting the unique documents. The architecture also allows the publisher to determine the identity of a recipient who has illegally,redistributed the document, without compromising the privacy of individuals who are not operating illegally. Two experimental systems ar e described. One was used to distribute all issue of the IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, and the second was used to mark copies of company private memoranda.