Combined robust and fragile watermarking algorithms for still images. Design and evaluation of combined blind discrete wavelet transform-based robust watermarking algorithms for copyright protection using mobile phone numbers and fragile watermarking algorithms for content authentication of digital still images using hash functions.

摘要

This thesis deals with copyright protection and content authentication for still images. New blindudtransform domain block based algorithms using one-level and two-level Discrete Wavelet Transformud(DWT) were developed for copyright protection. The mobile number with international code is used asudthe watermarking data. The robust algorithms used the Low-Low frequency coefficients of the DWT toudembed the watermarking information. The watermarking information is embedded in the green channel ofudthe RGB colour image and Y channel of the YCbCr images. The watermarking information is scrambledudby using a secret key to increase the security of the algorithms. Due to the small size of the watermarkingudinformation comparing to the host image size, the embedding process is repeated several times whichudresulted in increasing the robustness of the algorithms. Shuffling process is implemented during the multiudembedding process in order to avoid spatial correlation between the host image and the watermarkingudinformation. The effects of using one-level and two-level of DWT on the robustness and image qualityudhave been studied. The Peak Signal to Noise Ratio (PSNR), the Structural Similarity Index Measureud(SSIM) and Normalized Correlation Coefficient (NCC) are used to evaluate the fidelity of the images.udSeveral grey and still colour images are used to test the new robust algorithms. The new algorithmsudoffered better results in the robustness against different attacks such as JPEG compression, scaling, saltudand pepper noise, Gaussian noise, filters and other image processing compared to DCT based algorithms.udThe authenticity of the images were assessed by using a fragile watermarking algorithm by using hashudfunction (MD5) as watermarking information embedded in the spatial domain. The new algorithmudshowed high sensitivity against any tampering on the watermarked images. The combined fragile andudrobust watermarking caused minimal distortion to the images. The combined scheme achieved both theudcopyright protection and content authentication.