Robust Digital Watermarking by Discrete Cosine Transforms
In this paper, an image authentication technique by embedding message information into images is proposed. This technique is used for labeling digital pictures by hiding secret information into the images. A spread spectrum like Discrete Cosine Transform domain (DCT domain) watermarking technique for copyright protection of still digital images is analyzed. The DCT is applied in blocks of 8x8 pixels. The watermark can encode information to track illegal misuses. Two tests are involved in the ownership verification stage: watermark decoding in which the message carried by the watermark is extracted and the watermark detection, which decides whether, a given image contains a watermark generated with a certain key.