In this paper, we proposes a algorithm which is based on Discrete Cosine Transform (DCT) domain of original image. The technique of digital watermark can provide great useful guarantee for printed copyright. In order to embed the watermarking in a picture, firstly we divide the picture into 8×8 pieces and carry on the DCT transformation on per piece. Then we adjust each DCT coefficient of these pieces. Lastly we take out each of the parts of low frequency coefficient constitute watermarking signal. The watermark signal is imbed with different strength to the low frequency coefficient of the picture piece. The experimental results show the algorithm has very efficiency. The algorithm can be used in copyright and authentication purposes of digital image for the printed image.
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