Hey, got this out of the Subsim's SH4 guide, under the "how to complete a mission" heading, tells you how to complete a photo recon mission:
Photo.
You must travel to within 8 nautical miles of the objective then, while submerged, lock an enemy vessel in your periscope and press the menu bar button to take a photo. You may need a number of photos to complete the mission. You usually get 300 renown points for this mission.
Glance over the guide before your next patrol, on the following thread, its sort of like the game manual that should've came with the game! Tells you all kinds of helpful stuff I've found.
http://www.subsim.com/radioroom/showthread.php?t=108931
Hope this helps!