With powerful computer, high-resolution digital cameras, and sophisticated photo editing software, users can easily manipulate and alter digital images as they wish. Although good forgeries may not be perceptible by human eyes because no visual clues of tampering are left, they may leave some traces of digital tampering that could not be avoided in the media during tampering process. Most digital forgeries employ edge and region smoothing after the contents are manipulated or altered. In this paper, we describe how smoothing introduces disharmony between authentic regions and tampering regions, and then present a method to automatically detect smoothing regions at any part of an image that indicate possible tampering. The technique works well without any embedded information such as digital watermark.
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