MPEG-21 provides a framework within which many elements of multimedia are brought together. In particular, coded representations of content are juxtaposed with metadata descriptors and IPMP protection that apply to the content. This leads to a requirement for tools that can create and maintain (e.g. detect or extract) an association between content, metadata and IPMP elements within MPEG-21.

ISO/IEC TR 21000-11:2004 describes methodologies for the evaluation of two classes of technologies that can create and maintain such associations: "watermarks" and "fingerprints", when applied to audio content.