Abstract
Invertible watermarking has been introduced in the literature for the purpose of image authentication. We present in this paper 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.