The ubiquitous nature of digital network systems means large numbers of people can be copied digital contents without any cost. People can easily download images, videos and audio files and share them with other peoples or may also be modify the original contents. So there is an urgent need to provide protection of such digital media. There are many technologies to evaluate such problems like digital signatures. But there is a problem with these solutions because they require more bandwidth. Due to some limitations of previous technologies, a new technique came into being and this technique is called digital watermarking.