  This paper investigates the use of Structural Similaritys (SSIM) index on the
minimized side effect to image watermarking. For fast implementation and more
compatibility with the standard DCT based codecs, watermark insertion is
carried out on the DCT coefficients and hence a SSIM model for DCT based
watermarking is developed. For faster implementation, the SSIM index is
maximized over independent 4x4 non-overlapped blocks but the disparity between
the adjacent blocks reduces the overall image quality. This problem is resolved
through optimization of overlapped blocks, but, the higher image quality is
achieved at a cost of high computational complexity. To reduce the
computational complexity while preserving the good quality, optimization of
semi-overlapped blocks is introduced. We show that while SSIM-based
optimization over overlapped blocks has as high as 64 times the complexity of
the 4x4 non-overlapped method, with semi-overlapped optimization the high
quality of overlapped method is preserved only at a cost of less than 8 times
the non-overlapped method.
