When at the diner, you will find a trucker standing near one of the entrances (keep walking past the first one). Across the street is his truck, which he won't allow you to photo (you will get the option when facing it, even though it's across the street). You must talk to him to discover what kind of truck it is, then rewind and use the information to impress him. He'll then let you photograph the truck, which unlocks this trophy.
Any of the "optional photo" trophies can be easily obtained after finishing the episode by using chapter select and playing again in photo mode.