Abstract: The single watermark algorithms always merely have single function. In order to overcome the drawback, a multi-purpose dual watermark algorithm is proposed in the paper, taking advantage of the stability of singular values. It divides the original image into several blocks, and inserts robust watermark into their singular values. Then it inserts the fragile watermark into LSB in the space domain of previous watermarked image. Moreover, it designs a rule to distinguish malicious tamper from unintentional tamper. It tests not only robust watermarks robustness towards attacks, but also fragile watermarks influence towards robustness as well as the ability to tamper detection and localization. The experimental results show that the robust watermark possesses strong robustness to resist attacks, and that the fragile watermark is very sensitive to tamper and has good accuracy of tamper localization. Therefore it can achieve copyright protection and content authentication at the same time.