Abdelkader H. Ouda and Mahmoud R. El-Sakka, "Correlation Watermark for Image Authentication and Tamper Locations Detection", SPIE International Conference on Mathematics of Data/Image Coding, Compression, and Encryption IV, Vol. 4475, pp. 234 - 241, July 2001, San Diego, California, USA.
In this work, a new watermarking scheme is proposed to authenticate an image. This scheme is capable to detect the alternation locations, if any. The basic idea of this scheme is to uniquely represent a given image by a short string-sequence. This string-sequence is based on a correlation coefficient statistic; where the relationship between two adjacent image-rows/ columns is utilized. To generate this string-sequence a given image is divided into small blocks, where each block generates a different string-sequence. The Elliptic Curve Digital Signature Algorithm (ECDSA) is employed to sign these string-sequences to form an image dependent block-based watermark. Experimental results showed that the proposed watermark is highly sensitive to any alteration, and it can identify the location of any modified block in a given image.