Image forensics: spotting malicious tampering of images
Monday 18 May 2009
Xi Zhao, Professor Anthony TS Ho and Professor Yun Q Shi from New Jersey Institute of Technology, will present a paper on image forensics at the 16th International Conference on Digital Signal Processing (DSP 2009). The paper will appear in one of two special sessions on Multimedia Security and Forensics, organised by Professor Ho and Dr Chang-Tsun Li (Warwick).
Xi Zhao, Anthony TS Ho and Yun Q Shi. (2009). Image Forensics Using Generalised Benford’s Law for Accurate Detection of Unknown JPEG Compression in Watermarked Images. Proceedings of the 16th International Conference on Digital Signal Processing (DSP 2009).
In the past few years, semi-fragile watermarking has become increasingly important as it can be used to verify the content of images and to localise the tampered areas, while tolerating some non-malicious manipulations. In the literature, the majority of semi-fragile algorithms have applied a predetermined threshold to tolerate errors caused by JPEG compression. However, this predetermined threshold is typically fixed and cannot be easily adapted to different amounts of errors caused by unknown JPEG compression at different quality factors (QFs) applied to the watermarked images. In this paper, we analyse the relationship between QF and threshold, and propose the use of generalised Benford’s Law as an image forensics technique for semi-fragile watermarking, to accurately detect the unknown QF of the images. The results obtained show an overall average QF correct detection rate of approximately 99% when 5% of the pixels are subjected to image content tampering, as well as compression using different QFs (ranging from 95 to 65). Consequently, our proposed image forensics method can adaptively adjust the threshold for images based on the estimated QF, therefore, improving the accuracy rates in authenticating and localising the tampered regions for semi-fragile watermarking.