Statistical Methods For Digital Forensics

As a result of the widespread use of powerful image-processing software, it is increasingly easier to tamper digital images. For the time being, it has been possible to add or remove some important people or things to or from an image, leaving behind no obvious traces at the same time. Since digital cameras and digital vidicons replaced traditional analogue counterparts, it has become more and more urgent to identify digital images, to confirm image contents and detect their tampering. The traditional method to distinguish true or false images is to embed digital watermarks or signatures in digital images in advance. However, it still has a lot of weaknesses. Therefore it forms a new research direction to authenticate digital images that are embedded with no digital watermarks or signatures.Probably, an altered digital image cannot be authenticated. But, more often than not, some invisible clues may be left in the tampering process, because the tampering may disturb some underlying statistical properties of images. On account of this assumption, we propose two methods to detect tampered images in terms of different tampering forms:(1) A detection method based on the statistical properties of double-JPEG compression. This approach is used to detect previous quantification coefficients of double-JPEG compressed image pieces. First, identify some features of DCT histograms of particular coefficients due to double compression. Second, use SVM to estimate the original quantification coefficients from double-compressed images. The image areas with different quantification coefficients are worth our questioning. Finally, basing on many different sets of double-JPEG compressed images, use a series of experiments to verify the performance and reliability of this method.(2) A detection method based on image matching. This detection method focuses on the tampering type which is copying an image area then moving it to cover other important parts (Copy-Move forgery image). According to tampered image's sizes, two checking algorithms are put forth and their effectiveness and accountability are...