Ducks Easter Egg - Hidden Photo

Type ASKYAFFLE on the main menu to turn on the level skip key.
Get to level 29 (start in episode 2 and use # to skip levels).
Blow up the underside of the overhanging earth on the right of the level.
Walk the green duck under to the right and he should go through a hidden door which was previously hidden in the earth.
There's a quote (anyone know where this is from?) and a photo of some people from the credits.