Digital image watermarking has become a popular technique for authentication and copyright protection. However, many proposed image watermarking techniques are sensitive to geometric distortions, such as rotation and scaling. Rotation and scaling, even by slight amount, can make the decoder disabled unless the corrupted image can be rescaled and rotated back to its original size and original orientation. So it is very important to estimate the rotation angle and scaling factor correctly before watermark detection. In our approach, we propose a new way to estimate the rotation angle and scaling factor after the watermarked image has been scaled or/and rotated by using geometric moments of original image. The experimental results show that our method has a good robustness to wide rotation angle and scaling factor ranges.