Local image search against a source image?

Duplifinder looks like it does what you need. Just select the root folder as the one you want to search, and search all subfolders. It will give you a percentage as to how related they are, handles different formats, resolutions, etc.

You might also want to try SimilarImages and VisiPics. That last one might be the best of the lot.

I think this is what you are looking for: http://www.duplicate-finder.com/photo.html. It locates same or similar images on your hard drive and it's free.