a kind of multi-functional digital watermarking is provided
which can be applied to the copyright protection and user tracking of still images. The algorithm of the former
which implemented copyright protection
was based on the characteristic of systematic code in RS error correcting code. Aimed at client and Certificate Authority
this algorithm designed two different extracting methods
which ensured two different requirements of robustness. The algorithm of the latter
which implemented user tracking was based on SVD quantization and grouping inserting watermark. It reached the standard of strong robustness and could achieve 100% extracting with certain attracting. Experiment results the validity of this algorithm.