I just got back from picking up my photos at Walgreens.  

Isn't technology wonderful? <gush>

This is one of the photograph files I sent to Walgreens:

This is the print I got:

After spending almost 30 minutes at the photo machine with the young woman who works there we concluded that there is (apparently!) no way to put a (smaller) square on a rectangular piece of paper, leaving blank space on 2 sides.. 

Hardly rocket science, but that seems to be the way it is.