Selective Encryption of Still Image
Abstract: In some applications, it is relevant to hide the content of a message when it enters an insecure channel. The accepted view among professional cryptographers is that the encryption algorithm should be published, whereas the key must be kept secret. In the field of image cryptography, the focus has been put on steganography and in particular on watermarking during the last years. Watermarking, as opposed to steganography has the additional requirement of robustness against possible image transformations. Watermarks are usually made invisible and should not be detectable. In applications requiring transmission the image is first compressed, because it saves bandwidth. Then the image is encrypted. There is a need for a technique called selective encryption of compressed images with messages. Initially it aims of image encryption and various methods. Usually, during encryption, all the information is encrypted. But this is not mandatory, only a part of the image content will encrypted with messages in order to be able to visualize the encrypted Images, although not with full precision. This concept leads to techniques that can simultaneously provide security functions and an overall visual check which might be suitable in some applications like searching through a shared image database, distributed database for image storage etc., The principle of selective encryption is first applied to compressed images with messages . This technique is proven not to interfere with the de-coding process in the sense that it achieves a constant bit rate and that bit streams remain compliant to the JPEG specifications.