Abstract: A new content-based semi-fragile color image watermarking algorithm is proposed in this paper, which can be used for color image copyright protection and content authentication simultaneously. Firstly, the color image is converted from an RGB color space to a YCrCb color space. Secondly, the luminance component (Y) is decomposed by the L+1 level discrete wavelet decomposition, and the approximate wavelet coefficient matrix of the luminance component (Y) and the chaotic sequences are used to generate the content-based and secure watermark. Finally, luminance component (Y) and chrominance components (Cr and Cb) are decomposed by the L level discrete wavelet decomposition, and the watermark is embedded into color components (Y, Cr and Cb) by using the technique based on human visual system and block quantization. Experimental results show that our semi-fragile watermarking scheme is invisible and is robust to common image processing (such as JPEG compression, noise adding, filtering). The proposed watermarking algorithm is fragile to content modification (such as cropping), can detect effectively the tampered regions, and has a lower probability of missing or false alarm, compared with other popular semi-fragile watermarking schemes.