Abstract
In recent years, widespread use of the Internet increased the exchange of information and knowledge. However, the accompanying copyright and ownership problems became very critical to the success of digital content distribution. In order to solve these problems for digital content, information-hiding techniques have become more and more important in many application areas. Electronic watermark, which is also called digital watermark, is a branch of information-hiding techniques and it is a 68common function in several famous photo-processing application programs. Digital watermarking can be roughly divided into two types-visible marking and invisible marking. The former is commonly used in academic theses and stock photos, and the latter is popular in commercial document sharing, copyright protection, and bill antifaking. Both these types have their own special requirements, such as easy embedding, copy prevention, hard removing, robustness against tempering, and preservation of original information.