Abstract: According to the feature of digital image, the reason why traditional cipher algorithms are not applicable was analyzed, and the development of digital image encryption was surveyed. Some techniques, such as pixel permutation in space domain, encryption based on chaos, encryption in transform domain, image secret segmentation and sharing, encryption based on neutral network and cellular automata,encryption based on blind source separation,were illustrated,and the corresponding characteristics were analyzed and compared. At last, a large number of typical encryption algorithms were analyzed in detail to expose their weakness, and the future research direction was discussed.

Key words: Image encryption, Scramble, Chaos, Space domain,hransform domain