A Novel Copyright Protection for Digital Images Using the Gradient of Image Intensity

We propose a technique to protect digital images using the content-associated copyright messages generated by combining the original copyright message with the gradient of intensity of digital images. The proposed technique enables the distribution of the original copyright message without any distortion of original digital images by avoiding embedment of the original copyright message into images. In addition to the efficiency of generating copyright messages, it also has a relatively low computational complexity. To verify the propriety of the proposed technique, we performed experiments on its robustness to the external attacks such as histogram equalization, median filtering, rotation, and cropping. Experimental results on restoring the copyright message from images distorted by attacks show that more than 90%, on the average, can be recovered.