Perceptual Image Hashing

With the fast advancement of computer, multimedia and network technologies, the amount of multimedia information that is conveyed, broadcast or browsed via digital devices has grown exponentially. Simultaneously, digital forgery and unauthorized use have reached a significant level that makes multimedia authentication and security very challenging and demanding. The ability to detect changes in multimedia data has been very important for many applications, especially for journalistic photography, medical or artwork image databases. This has spurred interest in developing more robust algorithms and techniques to allow to check safety of exchanged multimedia data confidentiality, authenticity and integrity. Confidentiality means that the exchange between encrypted multimedia data entities, which without decryption key, is unintelligible. Confidentiality is achieved mainly through encryption schemes, either secret key or public key. Authentication is an another crucial issue of multimedia data protection, it makes possible to trace the author of the multimedia data and allow to determine if an original multimedia data content was altered in any way from the time of its recording. Integrity allows degradation detection of multimedia and helps make sure that the received multimedia data has not been modified by a third party for malicious reasons. Many attempts have been noted to secure multimedia data from illegal use by different techniques fields such as encryption field, watermarking field and perceptual image hashing field. The field of encryption is becoming very important in the present era in which information security is of the utmost concern to provide end-to-end security. Multimedia data encryption has applications in internet communication, multimedia systems, medical imaging, telemedicine, military communication, etc. Although we may use the traditional cryptosystems to encrypt multimedia data directly, it is not a good idea for two reasons. The first reason is that the multimedia data size is almost always much great. Therefore, the traditional cryptosystems need much more time to directly encrypt the multimedia data. The other problem is that the decrypted multimedia data must be equal to the original multimedia data. However, this requirement is not necessary for image/video data. Due to the characteristic of human perception, a decryptedmultimedia containing small distortion is usually acceptable. Deciding upon what level of security is needed is harder than it looks. To identify an optimal security level, the cost of the multimedia information to be protected and the cost of the protection itself are to be compared carefully. At present, many available image encryption algorithms have been proposed (Ozturk & Ibrahim, 2005; 2