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Techniques for protecting the Security of digital representations, and of analog forms made from them are presented. The techniques include authentication techniques that can authenticate both a digital representation and an analog form produced from the digital representation, an active watermark that contains program code that may be executed when the watermark is read, and a watermark agent that reads watermarks and sends messages with information concerning the digital representations that contain the water marks. The authentication techniques use Semantic informa tion to produce authentication information. Both the Seman tic information and the authentication information Survive when an analog form is produced from the digital represen tation. In one embodiment, the Semantic information is alphanumeric characters and the authentication information is either contained in a watermark embedded …