Close
It is a bit strange but when I see post about images dupes on imageboards, I never see the name of an extremely powerful (and open-source!)tool : imgseek, I think it's the only prog that search dupes by wavelet decomposition, and it's amazingly efficient to find exact dupes! (and this is the case here).
Everyone who has a large coolection of images (and so dupes...) should take a look at this!
You can even draw a paint and imgseek find an image that seems like your paint, it's really powerful!
P.S. : the version available on windows is 0.8.5, and is sometimes a bit unstable but the version 0.8.6 is better but run only under linux (but I think moe.imouto is run under linux right?)