Digital watermarking is an approach to manage multimedia digital information like images, as a data carrier to enclose copyright information, which might be either visible or invisible. If any copyright dispute arise, the ownership of the copyright can be verified from the information in the data carrier. Generally, digital watermarking system consists of two stages, namely watermark embedding and extracting. Likewise, the quality of the watermark system is evaluated based on the concealment, robustness, security and watermark capacity.
With regards to the robustness of watermark resisting attack, the digital watermarking approach is divided into three category such as robust, fragile and semi-fragile. Among these types, robust watermarks is widely used against image processing operations and apt for copyright and ownership verification. Fragile watermarks are responsive to modifications while suitable for authentication and integrity.
From the perspective of the various fields of hidden watermark, there are two types, spatial domain watermarks and transform domain watermarks. Between these types, the spatial domain watermarking algorithm directly modifies the original signal to hide the watermark information and though hiding watermark and the extraction process is simple here, the robustness is not as great as transform domain watermark.
