Quote - I'm not sure the tat guy is completely wrong, but unless I knew for sure, I would definitely get it in writing, for my own peace of mind. 

Whether he's completely wrong depends on the question that was posed to him.

"Will I get in trouble if I use art I downloaded from the web?" -- Very likely not -- agree with tat guy.

"Can I use copyrighted works in my products sold on Renderosity without getting permission from copyright holders?" -- Absolutely not -- disagree with tat guy. Tat guy probably doesn't know what Renderosity is or anything about its policies.

"Will I get sued if I infringe on someone else's copyright in commericial works?" -- Will my house in California suffer earthquake damage? Who the hell knows?  The question is how much risk you are willing and able to assume.

"If I take an image off the web and ink it on someone's arm, am I likely to get in trouble?" -- Probably not, but every reputable tattoo artist I have visited pays for subscriptions to tattoo flash sites, and I AM NOT going to allow anyone who disrespects copyright law to stick needles in my skin because I am going to wonder what other laws and regulations do they think they can just disregard?

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PoserPro 2014, PS CS5.5 Ext, Nikon D300. Win 8, i7-4770 @ 3.4 GHz, AMD Radeon 8570, 12 GB RAM.