Spatial watermark for image content authentication

This paper is focused on digital image authentication, considered as the process of evaluating the integrity of image con- tents relatively to the original picture and being able to detect, in an automatic way, malevolent content modifications. A computationally efficient spatial watermarking technique for authentication of visual information, robust to small distortions caused by compression, is described. In essence, content-dependent authentication data are embedded into the picture, by modifying the relationship of image projections throughout the entire image. To obtain a secure data embedding and extraction procedure, directions onto which image parts are projected depend on a secret key. In order to guarantee minimum visibility of the embedded data, the insertion process is used in conjunction with perceptual models, exploiting spatial do- main masking effects. The viability of the method as a means of protecting the content is assessed under JPEG compression and semantic content modifications. With the present system, robust- ness to JPEG compression up to compression factors of about 1:10 can be achieved, maintaining the subjective image quality after wa- termark insertion. At the same time, it is possible to detect and lo- calize small image manipulations. © 2002 SPIE and IS&T.