In the Gerudo Fortress there is a secret poster of Link from The Legend of Zelda: Skyward Sword. To find it, start in the room the Gerudo guards put you in when you get captured. Hookshot/Longshot up to the window above you, then jump to the closest ledge and go through the door. Go down the hallway into a small room (be sure to knock out both guards with arrows if you haven't received the "Gerudo Token" yet). Break the two crates in this room to reveal the poster.
Inside the Bombchu shop, go up to the counter and look at the left set of items in the shop. Another poster is along the wall on the left side of the screen.
On the second floor of the building where you catch the Super Cuccos is a bedroom. Enter and break the jars next to the wardrobe. Go into first person mode and look at the poster where the jars were to discover another poster.