How to reconstruct the history of a digital image, and of its alterations

This chapter reviews the operations undergone by the raw image and describes the artifacts they leave in the final image. The Internet, digital media, new means of communication and social networks have accelerated the emergence of a connected world where perfect mastery over information becomes utopian. Image manipulation can serve the interests of criminal or terrorist organizations as part of their propaganda. Noise estimation is a necessary preliminary step to most image processing and computer vision algorithms. Noise inconsistency analysis is a rich source for forgery detection due to the fact that forged regions are likely to present different noise models from the rest of the image. Image demosaicing leaves artifacts that can be used to find falsifications. The chapter seeks to determine the compression history of an image. It focuses on the JPEG algorithm, which is nowadays the most common method to store images.