To enable the source of an unauthorized copy of an information-bearing medium, such as a video DVD, to be traced, a compressed digital signal stream to be stored on the medium is altered to include "running marks," that comprise pixel blocks changing in position frame by frame and encoded with information...http://www.google.de/patents/US6285774?utm_source=gb-gplus-sharePatent US6285774 - System and methodology for tracing to a source of unauthorized copying of prerecorded proprietary material, such as movies
