Similarity-Based Watermarking for Sub-Sampling Images with Bacterial Foraging Techniques

Digital watermarking is an effective means for copyright protection or covert communication in the research field of information security. By using watermarking, the watermark bits are hidden into the multimedia content with the designed algorithm. And the watermarked contents, or the watermarked image in this paper, look almost identical to its original counterpart, while it still retains the capability to counteract intentional signal processing by others and keeps the existence of the hidden watermark. We employ the concept of sub-sampling and make use of the frequency coefficient similarities between the sub-images for effectively embedding the watermark. In addition, there must be requirements to keep both the embedded watermark alive and the watermarked contents acceptable. Here we make use of an optimization technique, called bacterial foraging, for obtaining an optimized watermarking algorithm with a properly designed fitness function comprising the possible requirements including the watermarked image quality and the capability for the existence of extracted watermark. Simulation results demonstrate the advantages and effectiveness of the proposed algorithm with the combination of sub-sampling and bacterial foraging.