Steps involved :

stroke    #  give black gradient highlight at  top right corder  and white gradient at bottom left corner. For this you have to select foreground-to-transparent with 50% opacity         # How to create  black shadow layer: use pen tool & dst and select around the photo with little in and out here and there after setting feather=4. Now create a new layer and fill with black and set opacity to 50%            # Finally you should tilt the photo by about 15 degree to have a realistic effect    #Useful links : http://www.brownbatterystudios.com/sixthings/2006/03/06/rapid-fire-1-photo-realistic/   and   http://www.pstut.com/tutorial-realistic-photo-print.html