Effectiveness of ST-DM watermarking against intra-video collusion

The impact of intra-video collusion on ST-DM watermarking is considered by analyzing the robustness of a constant watermark with respect to Temporal Frame Averaging (TFA). We theoretically show that, as opposed to spread spectrum watermarking, in the ST-DM case it is not sufficient that the same watermark message is inserted within each video frame to ensure resistance against TFA. However robustness can still be achieved by increasing the spreading factor r. Moreover the higher the correlation between video frames the better the performance of ST-DM. We also evaluate the impact of the dithering factor d upon watermark robustness. As a last contribution, we evaluate the impact of TFA on the quality of the attacked video, demonstrating that, unless motion compensated averaging is used, only a few frames can be averaged without introducing annoying artifacts.