Robust Undetectable Interference Watermarks
We propose a digital watermarking method for gray-tone images in which each watermark consists of a collection of single points and each point is encoded in the spatial domain of the whole image. The method is somewhat related to physical digital holograms and interference images. Reconstruction of such watermarks is based on a similar principle as the reconstruction of physical holograms.
While encoding a watermark in the spatial domain one of the major problems is to avoid a textured appearance due to the encoding scheme. We avoid a recognizable pattern by creating pseudorandom keyed watermarks, which resemble random noise.
The method proposed yields robust watermarks that are resistant against many attacks which preserve the distance between points (filtering, rotation, JPEG compressing). The watermarking scheme provides means for detection and reversal of scaling transformations, thus making the watermark resistant to this attack.
The original picture is not required for reconstruction. The watermark is quite hard to detect, which prohibits easy violation of watermark protection.
Our method guarantees exact reconstruction provided that the watermark image consists of a limited number of white pixels on a black background.
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