Thank you for making this an excellent program freely available, I appreciate the work that you've put into it.
One feature that I've always wanted to see in image indexing software is the ability to sort images by their histograms.
Sorting by histogram would group images of similar color schemes together, and to make identifying duplicate images easy.
Implementing a histogram search should be fairly straightforward, I have some ideas concerning implementation if you wish to discuss them feel free to contact me.
Thank you for your attention.