The rapid development of new information technologies has improved the ease of access to digital information. It also leads to the problem of illegal copying and redistribution of digital media. The concept of digital watermarking came up while trying to solve the problems related to the management of intellectual property of media. The concept of digital watermarking is derived from steganography. Both steganography and watermarking describe techniques that are used to convey information by embedding it into the cover data. However, steganography typically relates to covering point-to-point communication between two parties. Thus steganography methods are usually not robust against modification of the data, or have only limited robustness. Digital watermarking on the other hand should be robust against attempts to remove the hidden data. A popular application of watermarking is to give proof of ownership. It is obvious that for this application the watermark should be robust against any manipulation that may attempt to remove it.