Watermark based Image Authentication using Integer Wavelet Transform

Digital watermarking has immense importance in protection of copyright as well as authentication. In this work, a watermarking process utilising S transform is proposed with Haar wavelet that generate only integer coefficients. Initially, the forward transform of cover image generates four coefficient bands – HH, HL, LH and LL. The HH sub-band location map is randomized and watermark image is embedded using least significant bits (LSB) substitution of the coefficient. Additionally 256 bit SHA hash code of the watermark image is generated for authentication and embedded in the HL sub-band in a similar fashion. During extraction, watermark is extracted and SHA256 hash code is computed again. This new hash code is compared with extracted hash code for authenticity. The average PSNR (Peak Signal to Noise Ratio) observed for SIPI dataset is 65 dB and 59 dB with 8192 bit and 32768 bit watermark respectively with embedding rate of 2 bits per pixel. The results of the proposed merthod are checked against existing methods and it has been found superior in many cases.