Robust high capacity watermarking based on DCT and spread spectrum

Digital watermarking defined as invisible information hiding in a digital medium such as image, video, or audio mainly for ownership proving or information transmission. Watermarking is generally carried out in two forms namely spatial domain and frequency domain. Some algorithms require original image for extracting. There are other types of algorithm, called blind algorithms, which do not require any original image for extracting. In this paper, we apply blind algorithm to embed a high volume of hidden information by DCT method. Moreover, in order to increase the robustness we use spread spectrum to embed hidden information within DCT coefficients, where, the visibility of the image is ideally maintained. In order to demonstrate the robustness of the method against some common image processing operations such as compression, change in brightness and contrast, addition of noise, sharpening, blurring, filtering and etc, we have used Stirmark benchmark. In comparison with other researches the results show the validity of the method [4, 5, 8].