UBC Theses and Dissertations

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UBC Theses and Dissertations

Wavelet packets-based digital watermarking for image authentication Paquet, Alexandre


The rapid expansion of the Internet and the overall development of digital technologies in the past years have sharply increased the availability of digital media. Digital contents can be reproduced without loss of quality, but they may also be easily modified, and sometimes, imperceptibly. In many contexts, any alteration of image, video or audio data must be detected. Therefore, some work needs to be done to develop security systems to protect the content of digital data. Watermarking is accepted as a plausible candidate for such an application as it allows for the invisible insertion of information in a host by its imperceptible modification. This thesis is concerned with the protection of information contained in digital images. A novel, semi-fragile watermarking technique for the authentication of images is developed. Image protection is achieved by the insertion of a secret author's identification key in an image's wavelet packet (WP) decomposition. Rounding the mean of selected regions of WP coefficients embeds the binary key. To take maximum advantage of the host image's characteristics in the embedding process, an optimal quantization protocol is formulated. The image's verification is done without the use of the original unmarked image. The detection of unauthorized frequency or spatial tampering with the image is performed by a combined interband/intraband verification protocol. This new technique can detect malicious tampering with images, but stays unaffected by high quality JPEG compression.

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