[f33d5173]

The point is to embed a particular signature, which was generated randomly, in the image. The distance function discussed is the same as the popcount of the xor. It's well know that the xor of random data with correlated data is statistically random. Hence, however well correlated the signatures of unwatermarked images may be with each other, they would show no correlation with the signature of a watermarked image. That is, unless the watermark by extremely bad luck happened to be near one of these clusters the author discovered. This does represent a genuine flaw, but an extremely minor one, and one that can be easily mitigated with no changes to the underlying algorithm,