Codes and watermarks

This chapter analyses the principle of digital watermarking of images through the prism of the use of error-correcting codes in a very specific framework, namely the so-called robust watermark. It introduces a more original code and shows how a specific code can respond to a particular problem, the problem of cropping. Over the years, several watermarking paradigms have emerged due to the protection requirements of many applications. The chapter concentrates on so-called robust watermarking, which constitutes the classical application framework for the use of codes in watermarking. It discusses a simple use case based on watermarking by index modulation applied to color images. Error-correcting codes are powerful tools in information theory. The aim of robust watermarking is to optimize three properties in particular: the maximum amount of information that an image can contain, the invisibility of the mark and the robustness of the mark to image changes and, in some cases, security.