A Survey of Digital Watermarking Techniques

Watermarking is the process of inserting predefined patterns into multimedia data in a way that the degradation of quality is minimized and remain at an imperceptible level. Many digital watermarking algorithms have been proposed in special and transform domains. The techniques in the spatial domain still have relatively low-bit capacity and are not resistant enough to lossy image compression and other image processing operations. For instance, a simple noise in the image may eliminate the watermark. On the other hand, frequency domain-based techniques can embed more bits for watermark and are more robust to attack. Some transforms such as Discrete Cosine Transform (DCT) and Discrete Wavelet Transform (DWT) are used for watermarking in the frequency domain. In this thesis, we compare the DCT watermarking algorithms and especially the DWT watermarking algorithms based on robustness criteria. In other words, the robustness of different transform watermark algorithms is evaluated by applying different transforms.