In order to solve the problem that the encrypted image can be cracked easily and protect the copyright of related products, this paper adopts a digital blind watermarking algorithm based on block DCT transform. After the image is divided into blocks, the DCT transform is performed, and the spatial domain is transformed into the frequency domain. Then, we can embed and extract the watermark into the image. Finally, in the experiment about the digital watermarking algorithm based on wavelet transform domain, we found that the proposed algorithm can provide good watermark transparency for images with peak signal-to-noise ratio of 52.588 3 dB. And it has good performance to avoid noise and shear. This method has good robustness.