Duplicate images

I've been using Dup Detector to find duplicate image files (damn you 4chan). I've just found out that it doesn't detect .gif files though.
Are there any programs that work the same as Dup Detector, but can support gifs?

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>>18
Okay, please read what I asked again. md5sum would work to give a hash of the general file data, but I'm asking for some kind of an image analysis fingerprint, rather than just binary analysis fingerprint. It would say that a JPEG of Lenna Sjooblom is probably the same as a GIF of her. md5sum would not do this.