We've had a complaint from an artist who not only had his work posted in a thread without credit, it was linked from his website without permission. So every time someone loaded that thread, the graphic loaded, and his bandwidth got hit.
Please folks, don't do this. Credit folks, and don't steal their bandwidth. If you can't use a sharing service, then just post a URL. That will take them TO the site, if they want to see it...that's not stealing bandwith, that's upping the legit hits his site gets.
Also note that some artists will post that their art can not be reproduced, PERIOD, without their permission. Respect that, please. (Again, a link to their site is ok.)