The back and sides are covered to help make the ball python feel more secure. If your tank is sitting in a high traffic area of your home then this will help reduce stress to the snake from people walking by all the time.
I guess the background wallpaper may work. You want to attach it to the outside of the tank. That way it is easier to clean the inside of the tank. I used black construction paper and double sided scotch tape to attach mine. It has been on my same tank close to 3 years now with no trouble.