This may be different scans of the same picture or postprocessed versions of the same scan. Frames Different outtakes Annotations are handled by the blind spot feature. A certain number of mismatches is tolerated and regarded as result of limited manipulations. Maybe one should try to determine possible gamma corrections. Frames are naughty because they influence 12 of 16 sample pixels.
Outtakes are even worse because the lack of visible borders.
So let us assume 1e-20 as upper bound of random fault likelihood. With that builtin selectivity, the likelihood for a completely false duplicate in a collection of 100000 images should be about 1e-15 . This likelihood is valid only for faults that we would consider to be without any reason. For a collection that concentrates on a certain topic, there will be a lot correlation of colors. For black and white images the pessimisticly estimated likelihoot is about 1e-4.