Non-blind method of detection and localization of structural tampering using robust Hash-like function and similarity metric for digital images

Content preserving manipulations (CPM) in a digital image has been discussed subjectively in the literature so far. A number of ways of obtaining robust hash functions have been reported which claim to be robust against any content preserving manipulations and sensitive to structural tamperings. However, in many cases, one can make out these structural tampering just by viewing and comparing the two images, the original and the tampered image. We report an algorithm using robust Hash-like function and similarity metric by which even a very small but malicious tampering affecting only a few pixels of the digial image could be localized accurately. Results are shown in which locations of single or even multiple structural tamperings are successfully identified.