It is hard to accurately id some "type" images from a single photo. That being said, they look like ambrotypes to me. The sizes you gave would indicate they are "half plate" images. They are common portraits (not military, occupational, unique poses, etc.). As for value, it will be different, in different areas of the country. Just looking on completed listings on ebay, comparable half plate images seem to be selling for $20.00-70.00. IF it were a group photo or if it had a "Union" style case, the price goes up. If I had these images and were trying to sell them locally at auction, I doubt I would get $25.00. I might get $35.00-40.00 in an antique store. They are great finds! Doug