This paper present a novel easy and effective algorithm to plant digital watermark into digital images

this algorithm is different to general watermarking methods based on spread spectrum

because a new orthogonal base based on piecewise polynomial is constructed. The watermark based on this algorithm can resist energy loss caused by lose compression of digital image. In the first part of this pper

piecewise linear U system and its properties will be introduced respectively

corresponding graphs are shown

too. Following this part

how to generalize this algorithm to piecewise k degree U system is discussed; In the third part fo this paper

based on decompose digital image by piecewise linear U system

a kind of digital image watermarking scheme will be provided

the process of this algorithm is introduced step by step. By the end of this paper

some corresponding experimental results based on U system will be listed. The experimental results demonstrate the algorithm is reliable.