This study investigates a new method for adaptive watermark strength op-timization in Discrete Cosine Transform (DCT) domain. Watermarking is a method to embed secret information in the host medium. Optimal strength selection for watermark is the most critical aspect in the whole process and it had attracted many researchers in the recent past. In the proposed method watermark strength is intelligently selected through Particle Swarm Optimization (PSO). PSO helps in perceptual shaping of the watermark such that it is less perceivable to the human visual system. Proposed method shows promising results against different attacks, such as low-pass filter, high-pass filter, median filters, shifting and cropping the marked image. Experimental results for quanti-tative measures of imperceptibility i.e. Peak Signal to Noise Ratio (PSNR) and Structure Similarity Index Measure (SSIM) are presented. Robustness and imperceptibility tests re-veal better performance of the proposed method than the current approaches in practice.
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