A Polaroid guestbook.
The Polaroid guestbook has been around for a while, along with handing out disposable cameras.
Why not update this concept to a more modern idea, and use a #Hashtag printer service? Everybody has a cell phone these days, and picture quality is usually as good as a point and shoot.
All you have to do is take pictures with your cell phone, upload and tag them using Instagram or Twitter, and then head over to the kiosk to print them out. As an added bonus, the prints get formatted into a template that matches the event theme.