All five of the Photo Honshu missions in the mod are the same basic deal with the text of "Intelligence has requested an update on the enemy presence in [Yaizu, Ishinomaki, Osaka, Hiroshima, Tsursaki] harbor. Recon the area and, if possible, infiltrate the anchorage and photograph any enemy ships encountered." for the mission briefing, with slight differences between the wordings. The key phrase is "
photograph any enemy ships", but with a caveat. The photo score, which the player cannot see, is set to 20, so since the game uses a 10% score figure (I do not know why they used that "logic"...
), so you need a ship worth 200 renown points or more. Some merchants in the mod are not worth that much. so you'll need one of the big ones, a larger tanker, or passenger liner, or a CL Class and up, as far as warships go. If there are no ships of an appropriate type in the harbor, then you would have to leave and try again later, or just forget it altogether and go sink some ships. You would lose the 300 renown points for the mission objective, but you would make up for that with other ships sunk...
Now, the photograph stuff is a bit rather fiddly anyway, and you do have to use the periscope, and be on the full periscope screen. Make certain you have the full periscope menu displayed. Find a ship, lock on it, ID it if necessary, then hover your mouse over the "Camera" (Take Photo) button. If it lights, click it. If you see a flashing checkmark in the upper left of your screen, you have succeeded. If not, then go to the Objectives part of the Captain's Log clipboard, and see if there is a "Camera" icon to the left of the magnifying glass icon. If so, click on that, and look to see if the photo is any good. Maybe go back to the periscope, Lock on the target again, and attempt to take another picture. Or Lock on a different ship and try again.
Shore installations or docks do not work as photograph "Targets" in the game, only ships, and at that, only ships that are worth enough to trip the photo level set in the mission file, which the player usually cannot see. There are a few photo missions in the mod where the player is told to photograph a specific target or targets, but only a few.