Copyright protection of broadcast content has become an issue of great concern because digital broadcasting is increasingly used to deliver high quality visual and audio content. We analyze the existing copyright protection technologies and clarify why they cannot prevent illegal copies from being created through the analogue output of broadcast receivers. Illegally copied content can thus be re-digitized and distributed through the Internet and portable media. Digital watermarking that survives analogue processes effectively complements existing technologies. Four methods of using watermarking to detect illegal copies, copiers, and distributors are described and compared with respect to their implementation cost, detection ability, and ease of deployment. The technical requirements of the watermarking used in these methods are also clarified with respect to survivability against analogue processes, maintenance of image quality, and quantity of embedded information.
