Looking at watermarking
Like the watermark on paper where a translucent design is impressed on the paper during manufacture and visible when the paper is held to light, digital watermarking is the most discrete method of including additional material within the original data intended for consumption. In the case of audio data watermarking, the licencing, authentication and copyright information is the material within the audio data, imperceptible to the human ear but detectable by proper authorities. The widest use of digital watermarking is for copyright protection, labelling, monitoring, tamper proofing, and conditional access of the encoded data. A digital watermark can only be removed illegitimately with severe degradation in the quality of the data. A matching 'key' or a password of sorts is required to extract a digital watermark. See also the following useful resources: Overview of Watermarks, Fingerprints, and Digital Signatures Safeguarding Digital Library Contents and Users AudioKey AudioMark Giovanni ICE Audio Electronic Watermarking MusicodeŽ and Electronic DNAŽ SysCoP (System for Copyright Protection) | 
