Robust bit extraction from images

We describe an algorithm for robust extraction of bits from image blocks and a method for synthesizing a Gaussian pseudo-random sequence from those bits. The bits are extracted by thresholding projections onto random smooth patterns generated from a user-specified key. The extracted bits are further utilized to synthesize a Gaussian pseudo-random sequence that changes continuously with the image block yet depends sensitively on the secret key. The proposed technique is quite general and can be combined with the majority of oblivious watermarking schemes that generate watermarks from pseudo-random sequences. We anticipate that this algorithm will find applications in many oblivious watermarking schemes including secure data embedding into videos and watermarking images for tamper detection