数字式水印-------外文翻译.doc

Digital Watermark Multimedia Security 1. Control access such that only the right people can access to the multimedia content 2. Prevent illegal duplications 3. Authenticate the multimedia content are from the true sender (prevent impersonation and faked media distribution) 4. Images (Photo), Graphics, audio (music and song) and video can be protected by digital watermark 5. Watermark system makes use of the fundamental property of the human visual system/human auditory system – a visual (or audio) stimulus is less noticeable if superimposed over another large stimulus. Thus digital watermark make use of such properties in human perception and watermark can be added to media by noise masking/distortion masking techniques. A. Visible Watermark Visible watermark and copyright information can be added directly to the image. ??Overlay watermark adds words and logos to images to identify the copyright holder, the overlay watermark is irreversible and the image under the mark will be affected. ??Translucent watermark places translucent words and logos on the images to identify the copyright holder. The translucent watermark is reversible. If the watermark has been identified by hacker, the watermark can be completely removed. However, the translucent watermark causes less degradation in visual quality. ??Copyright information can also be added in header or comment sections in various multimedia format, e.g. JPEG and RIFF audio format. However, this information can also be easily removed by software. B. Robust Watermark Robust watermark is an imperceptible embedded data that are resistant to tampering. Application and Requirement of Robust Watermark Usually used as a proof of ownership of the electronic media. I. Audio Watermark should be robust towards amplification, truncation, sub-sampling, jittering, mp3 compression II. Image Watermark should be robust towards image filtering, scaling, rotation, cropping, Jpeg compression, gif conversion, horizontal flip, stirmark III.