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A semi fragile watermarking technique using a two level thresholding scheme for tamper detection is proposed. The proposed embedding technique uses two level IWT (integer wavelet transform) to embed the authentication watermark. The authentication watermark generated from the approximate coefficients is stored in the detail coefficients using least significant substitution to form the watermarked image. The proposed tamper detection technique for identifying attacks in the watermarked image is a two level thresholding scheme using normalized hamming similarity (NHS) and a tamper detection map. The performance of the proposed technique was evaluated for a variety of content preserving manipulations and malicious attacks. The proposed technique produces a better performance in terms of an increased PSNR (Peak Signal to Noise Ratio) of the watermarked image and by localizing the malicious attacks when compared to the existing techniques. The significant performance of the proposed semi fragile watermarking technique is due to the combined results from both the NHS and the tamper detection map which helps in localizing the malicious attacks and identifying the incidental manipulations. Also, the authentication watermark which is a copy of the original image helps in identifying the tampered regions in the attacked watermarked image.

Semi Fragile Watermarking Technique using IWT and a Two Level Tamper Detection Scheme