I also try and credit people for things I use in my image no matter if it's bought or it's free, but I know I miss things and like some have said when you have a ton in an image it can get a bit silly. I also never download freebies that have any restrictions on them, since I know I'll forget down the road. One thing I've often done is write the artist and thanked them personally for the model. Without the freebies I'd be royally screwed sometimes. I seem to always need something obscure. I once had a background I had made in Vue, claimed as their own and said it was created in bryce. So, I know how annoying that can be. I wouldn't have thought anything about it if he hadn't said anything at all about the background, but claiming it as his own work annoyed me. I might miss people in my credits, but I won't claim any model that isn't mine. Credit and copywrite two difference things.