Content is distributed via a network. Hierarchical watermarks are embedded in the content to prevent unauthorized copying of the content. In particular, a first digital watermark is embedded by a content source prior to distributing content to an intermediary distributor. The first watermark identifies...http://www.google.de/patents/US6804779?utm_source=gb-gplus-sharePatent US6804779 - Hierarchical watermarking of content that is distributed via a network
