With the proliferation of digital media such as images, audio, and video, robust digital watermarking and data hiding techniques are needed for copyright protection, copy control, annotation, and authentication of document images. While many techniques have been proposed for digital color and grayscale images, not all of them can be directly applied to binary images in general and document images in particular. The difficulty lies in the fact that changing pixel values in a binary image could introduce irregularities that are very visually noticeable. Over the last few years, we have seen a growing but limited number of papers proposing new techniques and ideas for binary image watermarking and data hiding. In this chapter we present an overview and summary of recent developments on this important topic, and discuss important issues such as robustness and data hiding capacity of the different techniques.
