First Quantization Table Detection in Double Compressed JPEG Images

In order to e ciently check the originality of images and videos from the all-day context, in the last ten years the scienti c discipline known as Image Forensics, whose goal is exploit the knowledge from the science of Image Processing to answer questions which arise in the forensic scenario, has developed at a growing rhythm. The objective of this doctoral study is to actively contribute to this research eld developing an approach devoted to recover the coe cients of the JPEG quantization matrix used to compress an image at the time of shooting (i.e., when the image has been created), when for some reasons this information is no more available in the Exif metadata. This scenario may include the primary quantization coe cients of an image that has been doubly JPEG compressed, or the retrievial of the compression matrix of an uncompressed image previously JPEG compressed, since in both these cases the values of the primary compression steps are lost. Once we are able to distinguish which is the \compression history" of a digital image, in particular the quantization matrix used for the rst compression, it is possible to exploit this information both for Image Forgery Identi cation and Image Source Identi cation, two of the main areas of Multimedia Forensics science. Although some papers allow taking an overview to the state of the art about Image Forensics methods, the need to include all the approaches in the various subsets of this research area necessarily prevents to explore in depth every one of them. Our purpose is to ll this gap regarding the approaches in the DCT domain, that has never been covered as a stand-alone topic