I found that using a rubber stamp on the back of photos ended up with two problems:1) It can take forever for the ink to dry.
2) Is the ink is really wet it is possible to bleed through the photo! Ouch!
I found what works best is to get some Avery labels like the 05660 laser, clear labels. Make your rubber stamp design in word or your favoriate program. Print up a few sheets of labels and your ready to mark all your photos.
It gives a much more professional presentation than a rubber stamp anyway. Plus you can change or customize each label if you wish.
Just don't print up too many at once.