I need to do a better job of this. I prefer using my own images, but when I do use stock, it's always images that have fairly broad or unlimited usage rights. That means I don't HAVE to, but I should, always give a link back.

It's funny; I've found my own stock images (sometimes properly licensed and sometimes stolen from those sites that properly licensed them!) with and without credit. I once found one of Paris published in a book on Paris for language learners! I was tickled pink! So you're right, it's good networking and just a really nice thing to do - no one had even told me, and I totally found those by accident. (Which I would not have, had they not given me credit.)