I figured as long as you don't say that it's your image or something, I don't see how it matters. Maybe link The source or artist if you really feel like crediting them.

Now granted, I can't say I'm "part" of that community or whatever, but I do know many artists don't like people "using" their work without permission. Understandable enough, but unless you're using a dedicated image hosting site like Deviant Art or Danbooru, finding the artist just from a pic is pretty hard. Then you get the types who [i]demand[/i] for you to link or whatever to a certain site, which has its own can of worms.

So long as your using the image in a nonprofit way like RPing, I don't see any legal reason you can't face claim or use other people's art. At worse you might be accused of piracy if the image normally has to be brought from the artist. But even that isn't punishable unless you're trying to turn a profit.