I posted this on the Favors board, but Etiquette gets much more traffic, and this is slightly related.
My photographer said she offers two types of photobooth shots. One is the traditional fun trio of photos, but the other is a family portrait photo. From what I gathered in our first discussion, it is completely free to the guests, both the picture given at the reception and a proof that can be used to print larger pictures or to create something like a christmas card.
I have never been to a wedding with a photobooth, so when the photographer mentioned it could work as a favor I was surprised, and didn't really know if it worked etiquette-wise, but the post below about favors made me think this is more common than I have seen.
I think that if more photos after the initial one at the reception had to be paid for, then I wouldn't use it as a favor, but assuming I am correct that it is all free to the guests, would you think this a good favor?