Well, for one thing, there was a stamp on the back with the photographer's name and the copyright symbol! That's your first clue! Coupled with the fact that it was very, very obviously posed in a studio, complete with studio accessories and careful fill lighting, and the serial numbers on the edges of the print (in the white borders that are covered when the print is matted and framed). On top of that was the unusual format - it was a 5" square, which is a common size for some studios around here to give out as samples before you buy the full package, especially of wedding photos; a non-professional photo printed at a regular department-store photo studio won't be printed in that size.