On detection of median filtering in digital images

FREE-DOWNLOAD M Kirchner of the SPIE, Electronic Imaging, Media , 2010
Digital image forensics has recently become a widely studied stream of research in multimedia security. Ubiqui- tous digital imaging devices and sophisticated editing software gave rise to the need for forensic toolboxes that can blindly assess the authenticity of digital images without access to the source image or source device or the aid of an auxiliary watermark signal. 3 When reasoning about the authenticity of digital images, it is necessary to have at least a rough working de nition of what constitutes a manipulation and what is considered to be a `legitimate’ post-processing. It is generally accepted that intentional manipulations of the image content (e.g., copy & paste operations or image splicing) are more critical and hence numerous forensic methods focus on de- tection of such `malicious’ post-processing. However, it is also bene cial to know as much as possible about the general processing history of an image, including content-preserving operations, such as compression, contrast enhancement, sharpening, and denoising. Even though such image processing primitives typically do not harm the authentic value of an image, they are of interest in a forensic examination of an image since they can a ect forensic methods in various ways. First, the actual state of an image prior to manipulation may in uence the set of tools we are using to analyze the image or our interpretation of the evidence derived from these tools. This is related to the eld of steganalysis, where, for instance, the choice of a suitable spatial-domain detector should be made conditional to the cover properties. 8 Second, certain post-processing steps may interfere with or diminish subtle traces of previous manipulations and thus decrease the reliability of forensic methods.