In this paper, a watermarking algorithm for ROI (Regions of Interesting) authentication and tamper detection is proposed. The watermarking is embedded in the DWT (Discrete Wavelet Transform) coefficients of the ROB (Regions of Background). The algorithm uses a hashing to detect whether the ROI of image is tampered, and then uses the watermarking to reconstruct the data of ROI. The experiment results show that the embedded watermark is perceptually invisible and robust to various image processing operations. Most importantly, the tampered place can be identified accurately.