I totally understand your confusion. In the Art Studio, using someone else's work without proper credit is most definitely against the rules. We have an entire section in the rules thread that goes over how to properly site an artist (thanks to Nina!) and their work with appropriate formatting. Artistic integrity on that front is something we take very seriously and look to uphold.
However, and I'm no expert this is strictly from my own personal observation, the rest of the forums (where one's art is not the focus), are a little different. There is no expectation that someone is posting art and claiming it to be their own, outside of the Art Studio. Because there's no claiming or profiting from the image, we take a laxer approach. Should you credit an artist if you post their work? Yes, always. Will we ban you if you post someone's edited Pokémon reaction gif in response to a thread? No.
Should you want to credit an artist outside of the Art Studio, finding out if the work you're using is available to be posted by someone other than the originator is the first step. Talk to the artist and ask if it's okay! We don't bite. :)
If there's a strict "please don't repost without permission", than we kindly ask you to respect the artist's wishes. If not, than please take the time to post a link to where you found the image you want to use. Name the artist or their dA/tumblr/whatever. It's that simple! :)
