Understanding geometric manipulations of images through bovw-based hashing

The increasing use of low cost imaging devices and the innovations in terms of media distribution technologies induce a growing interest on technologies able to protect digital visual media against malicious manipulations of the visual contents. One of the main problems addressed in this research area is the blind detection of traces of forgery on an image obtained through the internet. Specifically, in this paper we consider the context of communications, where malicious image manipulations should be detected by a receiver. In the proposed method, an image hash based on the Bag of Visual Words paradigm is attached as signature to the image before trans mission. The forensic hash is then analyzed at destination to detect the geometric transformations which have been applied to the received image. This task is fundamental for further processing which usually assumes that the received image is aligned with the original one, as in the case of tampering detection systems. Experiments show that the proposed approach outperforms state-of-the art methods by obtaining a good margin in terms of performances.