Well I went through a few definitions and read through alot of court cases ( I'm weird and actually find them interesting lol) Well it appears the legality of using picture is pretty generous. Under the fair use law, you can use copyrighted material for various purposes, one of them is teaching. So as far as the law goes, I can go copy all the pictures I want and put them on my site. Would I ever do that, of course not. but saying I cannot use your copy written content... actually I can.

So it basically comes down to moralist stand point of it. Obviously if you give me permission and give me your picture, there no problem.

things like, what if someone owns the animal, and someone else owns the picture, the guy who owns the picture gives me permission, but they guy who owns the animal wants me to take it down, where should I stand?

Someone gives me someone else's picture, that person wants it taken down and also wants to know who gave it to me, where do I stand?

You give me permission, then want it taken down later, where do I stand?

what other scenario might cause problems?