Sounds like fun!
There is a show like that on Australian mid-day tv, called Catch Phrase.
don't know of a script, but i'm sure it wouldn't be two hard.
You could make it really cool, by allowing dynamic uploads of pics and use gd to break it up into little bits.
But then again that would just be useless if you only wanted to just have a game for someone to play.
I would probably create an array with the key of each element in the array being the question and the value being the answer.
Each question would be on a seperate page, if the user answers wrong it does not continue, else it continues and reveals a part of an image, probably random.
I'm building a site for a client who wants a kids section, i'll build that and once i am done you can have it if you like. (good idea in exchange for code)