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Invertible watermarking has been introduced in the literature for the purpose of image authentication. We present a spread-spectrum invertible watermarking system which can be used to authenticate images in any lossless format, i.e. establish their integrity. A second application of invertible watermarking is multilevel access to watermarked images: depending on her clearance, the image user can "clean" the marks of more or less parts of the image, so as to gain in precision. Both applications make sense for precision-critical images (e.g. military, satellite, medical, quality control, reverse engineering images) whose copyright should still be protected to some extent.