Fecha de publicación: 24/10/2001 Fuente: Wipo "digitalization" A digital watermark is embedded into content for implementing copyright protection. The content is then distributed over a first transmission channel. A digital watermark signal to be superimposed on the content is transmitted over an encrypted second transmission channel. When the digital watermark is required, it is superimposed on the content and is then transmitted via, for example, an analog connection terminal. Alternatively, the digital watermark is decrypted and is obtained over the second transmission channel. The digital watermark obtained via the first transmission channel is then subtracted from the content, thereby removing the digital watermark. It is impossible for a third party to extract the digital watermark transmitted via the second transmission channel in meaningful form, thereby protecting the content form illegal use.