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Title: Active and passive approaches for image authentication
Keywords: Image Authentication, Image Forensics, Error Resilience, Error Concealment, Passive Image Authentication
Issue Date: 2-Aug-2007
Source: YE SHUIMING (2007-08-02). Active and passive approaches for image authentication. ScholarBank@NUS Repository.
Abstract: The generation and manipulation of digital images is made simple by widely available digital cameras and image processing software. As a consequence, we can no longer take the authenticity of a digital image for granted. This thesis investigates the problem of protecting the trustworthiness of digital images. Image authentication aims to verify the authenticity of a digital image. General solution of image authentication is based on digital signature or watermarking. A lot of studies have been conducted for image authentication, but thus far there has been no solution that could be robust enough to transmission errors during images transmission over lossy channels. On the other hand, digital image forensics is an emerging topic for passively assessing image authenticity, which works in the absence of any digital watermark or signature. This thesis focuses on how to assess the authenticity images when there is uncorrectable transmission errors, or when there is no digital signature or watermark available. We present two error resilient image authentication approaches. The first one is designed for block-coded JPEG images based on digital signature and watermarking. Pre-processing, error correct coding, and block shuffling techniques are adopted to stabilize the features used in this approach. This approach is only suitable for JPEG images. The second approach consists of a more generalized framework, integrated with a new feature distance measure based on image statistical and spatial properties. It is robust to transmission errors for both JPEG and JPEG2000 images. Error concealment techniques for JPEG and JPEG2000 images are also proposed to improve the image quality and authenticity. Many acceptable manipulations, which were incorrectly detected as malicious modifications by the previous schemes, were correctly classified by the proposed schemes in our experiments. We also present an image forensics technique to detect digital image forgeries, which works in the absence of any embedded watermark or available signature. Although a forged image often leaves no visual clues of having been tampered with, the tampering operations may disturb its intrinsic quality consistency. Under this assumption, we propose an image forensics technique that could quantify and detect image quality inconsistencies found in tampered images by measuring blocking artifacts or sharpness. To measure the quality inconsistencies, we propose to measure the blocking artifacts caused by JPEG compression based on quantization table estimation, and to measure the image sharpness based on the normalized Lipschitz exponent of wavelet modulus local maxima.
Appears in Collections:Ph.D Theses (Open)

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