Selecting optimal blocks for image watermarking using entropy and distinct discrete firefly algorithm

Image watermarking is the most promising method for preserving image copyright and its ownership identification. Watermark should have two contradictory properties of transparency and robustness. Location of embedding watermark in the image plays an important role in balancing these two properties. In this paper, a novel robust image watermarking scheme is proposed which uses combination of entropy and distinct discrete firefly algorithm (DDFA) for selecting suitable blocks to balance transparency and robustness. As image blocks numbers are distinct and discrete values, DDFA which is the modified version of firefly algorithm for optimizing distinct and discrete values is proposed and used to select optimal blocks. Hadamard transform applies on each selected block and watermark bits are embedded in Hadamard coefficients using average neighboring coefficients. Using Hadamard transform domain caused more robustness against signal processing attacks. The proposed method has been investigated by various standard metrics and experimental results showed its high robustness and imperceptibility; furthermore, there is a significant balance between these two properties.