Techniques for a Selective Encryption of Uncompressed and Compressed Images

This paper describes several techniques to encrypt uncompressed and compressed images. We first present the aims of image encryption. In the usual ways to encryption, all the information is encrypted. But this is not mandatory. In this paper we follow the principles of a technique initially proposed by MAPLES et al. [1] and encrypt only a part of the image content 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, for example, searching through a shared image database. The principle of selective encryption is first applied to uncompressed images. Then we propose a simple technique applicable to the particular case of JPEG images. This technique is proven not to interfere with the decoding process in the sense that it achieves a constant bit rate and that bitstreams remain compliant to the JPEG specifications. Then we develop a scheme called multiple selective encryption, discuss its properties and conclude.