ABSTRACT
If you hold a common banknote up to the light, a watermarked drawing appears. This watermark is invisible during normal use and carries some information about the object in which it is embedded. The watermarks of two different kind of banknotes are indeed different. This watermark is directly inserted into the paper during the papermaking process. This very old technique is known to prevent common methods of counterfeiting. In the past few years, the use and distribution of digital multimedia data has exploded. Because it appeared that traditional protection mechanisms were not anymore sufficient, content owners requested new means for copyright protection. The previous paper watermark philosophy has been transposed to digital data. Digital watermarking, the art of hiding information in a robust and invisible manner, was born. The recent interest regarding digital watermarking is demonstrated in Table 42.1, which reports the increasing number of scientific papers dealing with this subject. Today, entire scientific conferences are dedicated to digital watermarking e.g. “SPIE: Security and Watermarking of Multimedia Content”. Moreover, even if it is a relatively new technology, some industries have already commercialised watermarking products e.g. the widespread Digimarc.
