Forensically determining the order of signal processing operations

Currently, many forensic techniques have been developed to determine which processing operations were used to manipulate a multimedia signal. Determining the order in which these operations were applied, however, remains an open challenge. Understanding this order is important because it not only provides greater insight into a signal's processing history, but it can also be used to determine a forger's behavior patterns or provide insight into who manipulated a signal. In this paper, we propose a new forensic detection framework that can be used determine the order in which manipulations were applied to a signal. Additionally, we introduce the notion of a conditional fingerprint to describe how a manipulation's fingerprints can change under subsequent processing. We identify the conditional fingerprints of contrast enhancement followed by resizing, and use our framework to develop an algorithm to determine the order in which resizing and contrast enhancement were applied to an image.