Detecting Digital Tampering by Blur Estimation Dun-Yu Hsiao, Soo-Chang Pei Department of Electrical Engineering, National Taiwan University silverseraph@gmail.com pei@cc.ee.ntu.edu.tw Abstract With powerful computer and mighty software, seasoned users could turn digital media into what they want. The detection of digital tampering has become a crucial problem. In most of the time, digital tampering is not perceptible by human; however, some traces of digital tampering may be left in the media during the process. Based on this idea, we present a method in this paper that could reveal blurred regions that indicate possible tampering without any embedded information such as watermarking technique. Effectiveness and results will be presented, robustness would also be discussed. 1. Introduction Considering the making of digital image frauds, for example, face replacement, in order to produce a seamless doctored face, applying blurring is inevitable. Other than face replacement, skin smoothing and panorama are also blurring involved digital image tampering. Blurring is a very common process in digital image manipulation; it could be used to reduce the degree of discontinuity or to remove unwanted defects, ultimately, it is used to generate plausible digital image forensics. Hence if an additional blurring process applied on an image is detectable, possible fraud can be exposed even in a credible image. We will first introduce our blur estimation method. From the fundamentals of frequency domain knowledge about the mathematical model, we develop a scheme to detect blur regions for general images then modify it for identifying digital forensics. To illustrate the general effectiveness of this technique, we show results on naturally blurred images first to prove the effectiveness of our blur estimation method and proceed on perceptually credible forgeries applied manually smoothing, and then demonstrate the possibility to detect computer-generated objects in movie scenes by our blur estimation scheme. 2. Review on digital forgeries detection A study about how to verify digitally altered contents without the implementation of watermark becomes a novel and emerging subject. However, several researchers have carried out some representing results in different approaches, but these approaches are different from ours. Proceedings of the First International Workshop on Systematic Approaches to Digital Forensic Engineering (SADFE’05) 0-7695-2478-8/05 $20.00 © 2005 IEEE