Abstract: As an effect method to provide copyright protection for digital media, digital watermarking has drawn extensive attention recently. This paper proposes an adaptive image watermarking based on block classification. The algorithm splits the original image into blocks and classifies these blocks based on visual masking. Watermark components with different strength are inserted into some DCT coefficients according to the classification. The experimental results demonstrate that the watermarks generated with the proposed algorithm are invisible and robust against noise and commonly used image processing techniques.