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Content based image hashing using companding and gray code

Easily processing, storing, and propagating of digital images demand efficient and automatic techniques to identify and verify image contents. Image hashing is such a promising technique to represent and authenticate images without changing the content of images. The new robust image feature we use is the Morlet wavelet coefficients at feature points with the k-largest local total variations in images. The Morlet wavelet coefficients are pseudo randomly permutated such that image hashes have a small collision rate and are difficult to analyze by attackers. The Morlet wavelet coefficients are further quantized using companding technique and binarily coded using Gray code to form the final hash. Experimental results show the effectiveness and robustness of our method. The proposed image hash could have applications in image authentication and video signature. Copyright © 2010 John Wiley & Sons, Ltd.