Let me get straight to the point of this post: I find it difficult when people come with an image, obviously pulled from the internet, and want an exact tattoo of it.
I almost feel weird admitting this: I download music and TV shows from the internet for free - thank you usenet - but I balk when somebody wants an image recreated.
Here's the thing, I have less of an issue with turning a photograph or series of photographs into a custom piece. That's no problem. But when somebody comes in with a piece of art that has been pulled directly from, say, DeviantArt, I sort of feel bad.
Then I get over it and go about my business.
*Often I'll make a point to contact the original creator of the piece. I don't ask for permission though, I just tell them about the finished product.
