Recently a technique to detect digital information is attracted using a digital watermark technology by printed matter such as still images. This is the technique that are necessary when we want to embed information in a paper medium such as a magazine and a newspaper, the poster which a photograph is placed in in the limited space. Generally, a printed medium on the bulletin board is protected with a glass window to avoid influence on rain or dirt when the printed medium is posted up outside. In this paper, we considered how a glass window and rain drops on the printed medium affect a detection rate of embedded digital information or picture quality. We investigated that the glass window and rain drops affect what kind of effect on the frequency domain of the printed medium. Also, a most suitable PSNR level at the time of embedding were considered. As a result, it is concluded that a most suitable SNR is around 27.5dB.
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