Abstract: A novel zero-watermark algorithm is proposed based on subsampling in hybrid
transform domain for the copyright protection of image dates. In this method, the host image is
performed with Non-Subsampled Shearlet Transform (NSST) firstly, and low-frequency
component is divided into four sub-images by subsampling, then block processing is done to
every sub-image. Finally, the zero-watermark is constructed by judging the numerical relationship
between the DC coefficients of two special blocks from different sub-images randomly.
Experimental results show that the method is very robust to common attack operations such as
Adding noise, JPEG compression, Cropping and so on.

Key words: zero-watermark, subsampling, Shearlet transform, DCT