Optimized spread spectrum watermarking for fading-like collusion attack

An optimized spread spectrum (SS) image watermarking scheme robust against fading-like collusion attack is proposed using genetic algorithms (GA) in multiband (M-band) wavelet decomposition. M-band decomposition of host offers advantages in better scale-space tiling and good energy compactness. This makes watermarking robust against frequency selective fading. On the other hand, GA would determine threshold value for the host coefficients (process gain i.e the length of spreading code) selected for watermark casting along with the respective embedding strengths. An objective function is developed from the weighted combination of local and global embedding distortion (imperceptibility), normalized process gain and robustness measure to balance among conflicting requirements. Simulation results show convergence of GA and validate relative performance gain achieved in this algorithm compared to the existing works.