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Image authentication by exact histogram specification

The paper proposes a spatial domain watermarking scheme for image authentication and, in case image content has been changed, for localization of the altered area. A pseudo-random set of pixels is selected by using a secret key and is marked with a visually meaningful watermark by exact histogram specification. The exact recovery of the watermark authenticates the image. Specially designed watermarks are used to locate the altered area. Image visual aspect as well as image histogram are preserved. The approach addresses gray level and color images as well.