An algorithm for removable visible watermarking
A visible watermark may convey ownership information that identifies the originator of image and video. A potential application scenario for visible watermarks was proposed by IBM where an image is originally embedded with a visible watermark before posting on the web for free observation and download. The watermarked image which serves as a "teaser." The watermark can be removed to recreate the unmarked image by request of interested buyers. Before we can design an algorithm for satisfying this application, three basic problems should be solved. First, we need to find a strategy suitable for producing large amount of visually same but numerically different watermarked versions of the image for different users. Second, the algorithm should let the embedding parameters reachable for any legal user to make the embedding process invertible. Third, an unauthorized user should be prevented from removing the embedded watermark pattern. In this letter, we propose a user-key-dependent removable visible watermarking system (RVWS). The user key structure decides both the embedded subset of watermark and the host information adopted for adaptive embedding. The neighbor-dependent embedder adjusts the marking strength to host features and makes unauthorized removal very difficult. With correct user keys, watermark removal can be accomplished in "informed detection" and the high quality unmarked image can be restored. In contrast, unauthorized operation either overly or insufficiently removes the watermark due to wrong estimation of embedding parameters, and thus, the resulting image has apparent defect.