I granted Guest access to someone today, and shortly after that I had photos showing up on the home page of the tree. How is that possible? The guest said it allowed her to add photos and names. My tree has been up since 2012 and that has never happened before.

Check if you made the person a guest, or, in error, a member. If you made her a "member", by mistake, she could enter a limited amount of info and photo's. As a "guest - that should not be possible. . Its all in the instructions. Members can but only add or update their direct relatives (parents,children,siblings and spouse)