Contrary to popular opinion, the use of paper in our society will not disappear any time during the foreseeable future. In fact, the use of paper continues to grow rather than decline. It is certainly true that as individuals, we may be printing less than we used to. And the role of paper has been transformed from the archival record of a document to a convenient and aesthetically appealing graphical user interface. The use of paper is now intimately linked to the electronic systems that capture, process, transmit, generate, and reproduce textual and graphical content. Paper can be thought of as an interface between humans and the digital world. If this interface is not secure, the entire system becomes vulnerable to attack and abuse. Although paper is read by humans in the same way that it has been for millennia, and has had the same fundamental form and composition for almost that long as well, the technologies for printing and scanning documents and capturing their content have evolved tremendously, especially during the last twenty years. This has moved the capability to generate printed documents from the hands of a select few to anyone with access to lowcost scanners, printers, and personal computers. It has greatly broadened the opportunities for abuse of trust through the generation of fallacious documents and tampering with existing documents, including the embedding of messages in these documents.