Digital image forensics for global, local, and offine forgeries

Abstract

With the development of highly sophisticated forms of information technology, digital images are commonly used in our life. The benefits of digital images, such as the ease with which they can be edited, shared, and stored, have led people to use digital images in place of analog images. At the same time, the very nature of digital images, which can be easily manipulated or distributed, brings into question many of the positive aspects associated with these types of images. Furthermore, easy-to-use imaging devices accelerate the acquisition of high-quality fake documents such as counterfeited currency, gift vouchers, and so on by scanning and printing process. Therefore, this dissertation proposes forensics techniques as countermeasures to solve various global, local, and offline forgeries.

At first, the dissertation presents a forensic technique that estimates the linear transformation of an investigated image. The linear transformation, such as rotation, scaling, or any combinations of geometric attacks, is among the most common forms of global image manipulation. We exploited the periodic properties of interpolation by the second-derivative of the transformed image in both the row and column directions. Both the magnitude and phase information of the derived signals were analyzed to estimate the transformation matrix accurately. Empirical evidence from a large database of manipulated images indicates the superior performance of the proposed method. Subsequently, we propose a reinforcement scheme to complement conventional image watermarking system by analyzing the periodicity of interpolation. Digital watermarking is one of the most fundamental techniques to protect copyright of digital images. However, it is rarely possible to develop a watermark system robust to all kinds of attacks. Instead, lots of watermarking systems are still weak against even simple linear transformation. Therefore, in this dissertation, we propose an enhancing method to detect the...