I have a dozen generous friends who are photographers and they have given me permission to use their photos for my cards.  I wish there was a one line space on the BACK of the card where you could put something like, "Front image by John Doe".  I know their info shows on the Artist's Notes, but card recipients never see that.
 
Currently, I am writing their name in the photo itself, but I think it seriously detracts from the look of the front image, especially since I have to put their name inside the margin guidelines.  When I had a card delivered to me, the photographer's name "floated" about a quarter inch above the bottom of the card.  You never know exactly where the bleed lines will be cropped.
 
Please consider adding just one line on the back of the card to credit the artist who provided the front image.  I know a lot of people use public domain artists and would like to credit them as well.  Thanks!

That's a great idea..

Thanks for the great ideas!  While I don't mind placing the credits as you have suggested for now, I would love to just put them on the back.  There are other card companies that have descriptions on the back about the front image.  I just want a few words, even if it's in tiny print!