I don't know if this is possible or desirable - I was curious if there is a way we could add a field that will print on the back of the card that incorporates a short summary about the image on the card.  I'm thinking along the lines of postcards that have a short paragraph mentioning if the card is of a particular subject and location.  It might be nice to have this short little piece on each card.  
 
Example: Photo of sunset over town dock in Stoney Creek, Branford, CT.
 
Stoney Creek, for example, is a popular tourist stop in my town and if I were to create such a photo and use it for a card, it might be nice to have this actually printed on the card itself.  I suggest this as a friend of mine loves to send cards to a friend in Hawaii and she always appreciates knowing some background about the image - photo, drawing, whatever it may be.

I don't know if I'd personally want it on the inside of the card - I would rather it be on the back - perhaps under my store name as a short note... but that's just me... I think putting something like that on the inside would cause clutter.

I have a lot of photographer friends who allow me to use their images and I'd love to give them credit on the back.  Excellent idea!