Blind Digital Watermark Based on Discrete Fourier Transformation

Abstract

The policy and security of digital images are concerned by all artists. Embedding blind digital watermarks to images is an effective solution to such problem. The existing blind digital watermark techniques for images are usually based on the spatial domain method, such as some build-in tools in some software like Photoshop. Those methods' imperceptibility is good, but the robustness is dissatisfactory. Therefore, blind digital watermark based on the frequency domain is becoming popular nowadays. The use of the frequency domain-based techniques can not only keep the imperceptibility but also ensure good robustness and non-removability. According to the reasons mentioned above, this thesis presents a frequency domain-based blind digital watermark technique. This method uses basic discrete Fourier transformation to transform an image to the frequency domain and then embeds a digital watermark. To increase the security, we also introduce some methods to encode watermarks before embedding them to the images. We conduct some experiments by applying the technique to some images with different watermarks. In the experiments, it can embed blind watermarks with the least effect on the quality of the original image and can also successfully extract watermarks from the watermarked image. The results show this technique is highly useable. We also conduct some experiments to simulate the attacks. This technique also shows great robustness after many kinds of different attacking methods.