Fingerprints are unique strings or IDs representing the actual audio material in order to reliably identify the work. Some fingerprints are catalog numbers issued by the original creator or by metadata providers like Clipland. Some fingerprints are generated by calculation against the raw audio waveform, while others being generic random strings rely on an external index or database. These fingerprints or unique identifiers are in concept related with watermarks, message digests and file hashing or digit sums.