Singular Value Decomposition (SVD) is a special matrix transform with very good properties. This paper makes full use of the properties of SVD, and proposes a new quantization watermarking algorithm based on block SVD and a new spread spectrum watermarking algorithm based on block SVD. Both of the two algorithms embed watermark by altering the largest singular value of each data block, thus they can adjust the block size according to the amount of the watermark to be embedded, and their complexities are very low. The quantization watermarking algorithm is a method that makes use of the side information, and it’s a blind algorithm. The experiment results show that watermarking algorithms based on block SVD are very robust to usual image manipulation attacks, especially the quantization watermarking algorithm.