Image watermark extraction for captured image with partially glass reflection

This paper addresses a problem of detecting watermark signal from watermarked printed image behind a glassy object. By considering a situation where an image owner tries to extract his/her embedded watermark from a camera-captured image having unauthorized image inside, such image will always include RST (rotation, scaling, and translation) and perspective distortions from the processes of printing and camera-capturing, which consequently affect the accuracy of the extracted watermark. The situation becomes worse when the image is captured through the glassy object, and some lights reflect off the glass surface. In this paper, we thus propose a method to extract a watermark from a camera-captured image contained partially glass reflection. Basically, the image alignment technique based on projective transformation is applied to diminish both RST and perspective distortions due to printing and camera-capturing processes. Next, undesirable reflection reduction technique based on gradient field is introduced to reduce unwanted reflection in the cameracaptured image, before performing the watermark estimation sub process. The experimental results show effectiveness of our proposed method and possibility to implement it in other watermarking schemes.