Press space to start. User the arrow keys to move around the zoomed image. Tap the x and z keys to change.Press 1, 2 or 3 to toggle between the backdrops behind the main image available. Also, once you have changed the size of the image you cant use the arrow key movement anymore, so press the green flag.
NOTE THAT ONCE YOU HAVE TOGGLED BETWEEN THE SIZES THE ARROW KEY MOVEMENT WONT WORK! (why, don't know. anyone with a reason comment below)
