Active watermarks and watermark agents

Abstract

Techniques for protecting the security of digital representations, and of analog forms made from them. 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 watermarks. The authentication techniques use semantic information to produce authentication information. Both the semantic information and the authentication information survive when an analog form is produced from the digital representation. In one embodiment, the semantic information is alphanumeric characters and the authentication information is either contained in a watermark embedded in the digital representation or expressed as a bar code. With the active watermark, the watermark includes program code. When a watermark reader reads the watermark, it may cause the program code to be executed. One application of active watermarks is making documents that send messages when they are operated on. A watermark agent may be either a permanent resident of a node in a network or of a device such as a copier or it may move from one network node to another. In the device or node, the watermark agent executes code which examines digital representations residing in the node or device for watermarked digital representations that are of interest to the watermark agent. The watermark agent then sends messages which report the results of its examination of the digital representations. If the watermarks are active, the agent and the active watermark may cooperate an the agent may cause some or all of the code than an active watermark contains to be executed.

1 . Apparatus for responding to watermarks in digital representations in a system that processes the digital representations containing the watermarks, the apparatus comprising: 
 a watermark agent that includes a program which, when executed, reads a watermark in a digital representation and performs an action involving information contained in the watermark; and    a watermark agent engine that executes the watermark agent, the digital representations whose watermarks are read by the watermark agent being neither fetched into the system by the watermark agent nor fetched into the system for the watermark agent.    
   
   
       2 . The apparatus for responding to watermarks set forth in  claim 1  wherein: 
 the system that processes the digital representations is a node in a network; and    the system that processes the digital representations receives the watermark agent from another node in the network.    
   
   
       3 . The apparatus for responding to watermarks set forth in  claim 1  wherein: 
 the system that processes the digital representations is a node in a network; and    the action performed by the program being executed is sending a message to another node in the network.    
   
   
       4 . The apparatus for responding to watermarks set forth in  claim 1  wherein: 
 the action performed by the program being executed is sending a message to the system that processes the digital representations.    
   
   
       5 . The apparatus for responding to watermarks set forth in  claim 1  wherein: 
 the system that processes the digital representations responds to the message by altering the manner in which it processes the digital representation whose watermark was read by the watermark agent.