Look for the camers icon at the control bar when you are at the periscope station. If you get a good lock it will light up then click on it. You may have to get more than one photo of what is out there in order to complete the mission. Also make sure you are close enough to the Icon on the map. I forget whether it is 500 or 1000 yards. Save your game once you complete it successfully then sink the bastards....
