Back in 94/95 at Goodwill I was thumbing through some random book and there was a 8x10 photo of an orangutan sitting alone in a metal cage. It wasn't a part of a book and the book wasn't about apes or zoos or anything related, it was just a random photo someone had stuck in there. I asked how much for the photo, and they gave it to me. I still have it in a box in my office.
IME it's pretty common to find stuff like this (photos, receipts, napkins, etc.) used as impromptu bookmark and "swallowed" at some point so not obvious it's there.
