This book deals with digital watermarking, which is defined by the authors of this book as the art of hiding auxiliary information in digital data in a secure, robust and imperceptible fashion. Digital watermarking as a topic has a long history, but before 1995 publications in scientific literature were almost absent. From 1995 onwards however the number of publications on watermarking has been steadily increasing. Today a number of workshops and conferences on this topic exist; also a number of scientific journals on watermarking have been published. This renewed scientific interest in digital watermarking has led very quickly to industrial interest, as well. In 1996 the Copy Protection Technical Working Group, a voluntary consortium consisting of the movie industry, the IT industry and the consumer electronics industry, issued a call for watermarking technologies for the purpose of copy protection of DVD-Video. A few years later the Secure Digital Music Initiative issued a similar call, in this case focusing on copy protection of digital music. These two efforts have been only partially successful: copy protection based on digital watermarking is not (yet) implemented on a large scale in any type of consumer device. This current failure of watermarking, to live up to its expectations, finds its cause in a large number of reasons, ranging from legal considerations and system aspects to the relative immaturity of watermarking as a technology.