Hard times are on the way for Internet pirates. The German portal provider Librie.de is now using digital watermarks to protect
their audio data. When an audiobook is downloaded, invisible marks are embedded in the file as a permanent code identifying the legitimate purchaser.
The protection system employed comes from the
Fraunhofer Institute, where researchers have developed a technology for hallmarking audio data. The MP3 files are modified so slightly that it is imperceptible to the human ear. This automatic process is comparable to the insertion of noise or a minor distortion of individual frequencies. A software program is able to read the markings in subsequent copies of the file. This allows online content providers to hide a customer reference code, for example, "between the lines". The end user remains totally unaware of what is happening.
The idea is, if ever an illegal copy appears somewhere on the Internet, this watermark leads directly back to the original purchaser. And if you want to believe the researchers, the protection even survives transmission on analog broadcast media or tape recordings made from a loudspeaker.
(Attached image shows how the information concealed in the watermark of an audio file lies in the mid-frequency range of human audition)
[via
Fraunhofer press-release]