A robust digital watermarking technique with improved performance under JPEG compression

Abstract

Digital watermarking is an important technique to protect copyrighted multimedia data. This technique works by hiding secret information into the images. Therefore, it can be used to discourage illicit copying or distribution of copyrighted materials. In this paper, we propose a robust frequency domain digital watermarking algorithm for still image based on discrete cosine transformation. Adjustable parameters are introduced during the watermark embedding process, which adaptively change the JPEG quantization factor, as well as the depth at which the watermark is embedded. The proposed watermarking technique still maintains its validity under certain image processing operations such as low pass filtering, image cropping, etc. Compared with previous method, however, it has improved performance under Joint Photographic Experts Group (JPEG) compression attack. The extracted watermark maintains its high quality in terms of normalized correlation even under a high JPEG compression ratio.