Cats lick uncovered pictures because they like the taste of the emulsion used in photodeveloping shops. The emulsion smells like rotten fish, guess some cats like to eat stinky stuff. It's not real healthy for them to do this a lot (once in a while probably won't hurt) but you will definitely want to put your pictures out of Kitty's reach. After awhile, the pictures start looking really shopworn. We had an orange tabby that would lick unprotected photos 'til they were tattered, so we learned to put them away.