It is actually not all that uncommon for cats to lick photographs - some evebnlike glue, like KoKo in The Cat Who series tho I suspect KoKo's behavous might well be based on the real life Koko.
YY adores those blasted green grocery bag ties and I have to waatch her like a hawk because one of my fears is hthat she might accidentally swallow one!!
Here are two articles that MIGHT help:
http://66.102.7.104/search?q=cache:I...on+walls&hl=en
http://cats.about.com/cs/behaviorali...hycatslick.htm