The image will show up in your VF2 game provided you rename it HammockStd.png, place it in the Furniture folder, and purchase a hammock from the store (or already purchased one). Try it out. Place a peep in it and see how you like it. Make sure you save a copy of the original HammockStd.png in a safe place BEFORE placing this one in your game, in case you want to change back (same goes before installing any mod).