As a result of the development of computer network technology, communication of information through personal computer is becoming more convenient. Meanwhile, it also gives hackers opportunities to attack the network. Therefore the communication security is now an important issue for multimedia communications. In recent years, many image cryptosystems are proposed. As encryption process is applied to the whole image, it is difficult to improve the efficiency. Encryption of digital image processing becomes more and more important for Internet data transportation and many methods can be applied for the processing.
In this paper, we survey on existing work which is used different techniques for image encryption and we also give general introduction about cryptography.