- Mark-and-trace DRM schemes try to put a unique, indelible mark on each legitimate copy of a work, so that any infringing copies found later can be traced, with the aid of the mark, back to the legitimate copy from which they originated. Such schemes have fallen out of favor recently, because of two problems.
First, the mark must really be indelible. If an adversary can remove the mark, the resulting "scrubbed" copy can be redistributed with impunity. Nobody has figured out how to make marks that can't be removed from music or video. Past attempts to create indelible marks have failed miserably. A notable example is the SDMI watermarks that my colleagues and I showed were easily removed.
Second, blaming the buyer of an original for all copies (and copies of copies, etc.) made from it just isn't practical. To see why, suppose Alice has a big collection of music on her laptop. Then her laptop is stolen, or somebody breaks into it electronically, and all of her songs end up on millions of computers all over the Net. What then? Do you take all of Alice's earthly possessions to compensate for the millions of infringements that occurred? (And if that's the policy, what sane person will buy music in the first place?) Or do you let Alice off the hook, and allow burglars to defeat your entire DRM scheme? Nobody has a plausible answer to this question; and the Fraunhofer people don't offer one.