Well, in all honesty, although it's a funny and great idea, I don't think it will work out somehow!
Not everyone is online everyday, or might not get an opportunity to get a festive photo to upload. Some may be shy, and not WANT to add a photo, and might feel excluded. We don't want that to happen. 
I think Lotties idea was a good one. Geoff can hold the main calander and open the door daily, and we can all guess what the chocolate shape is! Or the picture behind it. We all love guessing games!
Just a thought. 