Nonorthogonal DCT block convergence for JPEG-75 forensics

Many forensic techniques recently tried to detect the tampering and manipulation of JPEG compressed images that became a critical problem in different imaging applications. Some techniques indicated that a knowledge able attacker can make it very hard to detect image tampering, while others indicated that portions of the compressed image that has been compressed at different compression parameters can be detected, if they are recompressed after changing some of these parameters. In this project, we pursue the idea of analyzing forensically suspect-able images to detect forgery. We study the effect of adopting Nonorthogonal Discrete Cosine Transform (NDCT) that is highly utilized in efficient media implementations, in detecting if different parts of the image have been modified. This is performed by measuring block convergence of different image parts and detecting its stability after recompressions.