I had a friend that goes through my pennies trying to find valuable rare pennies. Instead of looking at each one could a optical character recognition program be used to flag coins?
Without seeing the coins it's not easy to give a unique solution. A possibility would be: Use the Hough transform to detect circles (the coin). Then do some open/close operations to get blocks of text, maybe apply Hough transform again to detect straight lines and finally, do the OCR.
Another possibility is to do template matching. If you have pictures of other similar coins then you can first find the coin orientation and then target the characters that you want to recognize.