If you have a scanner and a program like photoshop elements, try scanning the back, and then using the enhancement tools in the program to increase contrast, or to change the lighting/shadows. If you have a
Mac computer, IPhoto has those tools standard.
The other thing you might do is put some of them on the
Sangamon message board with the family names that you think they belong to, and see if anyone else can help. I have had some luck with that approach.