They're making small changes every day. It wasn't until the head had been gnawed clean that I noticed, though: prior to that I was thinking "cool, I keep noticing new details in this picture!" but it was only after using Gimp to look at the differences that I realised they'd quietly changed loads of other stuff... pretty cool, really.
BTW I'm keeping each pic of the advent calendar on my hdd, just for the memory of the event
And they're amazing as wallpapers, too.
