Copyright is complicated and we’re going to make it uncomplicated right now. Move over, DeviantArt.
Copyright is a law that gives ownership of work to creators, whether they be painters (digitally or physically), musicians, or writers and outlaw others from stealing their hard work and profiting from it.
All artwork is immediately placed under copyright law when it becomes something tangible. Whether it’s written on paper or messaged to someone online, that idea becomes yours. However, ideas are things that cross over easily with other peoples’ ideas so copyright of ideas is still a very murky area. Pictures, paintings, dances, music, writing, etc. are all protected by copyright and are automatically owned by the artist. Copyright law prevents anyone but the artist from illegally using or redistributing their work if they do not wish it (which is mostly the case).
The creative commons license is a set of rules enforced by copyright law that allow non-artists use of artists’ work. No artwork is automatically put under the creative commons licence without artist consent, meaning no artwork is immediately available to the public for any use aside from looking at it. There are a lot of really nice artists and photographers who put their work under the creative commons license because they want to share their art with everyone around the world. However, just because you can’t see the work under creative commons or don’t know if the art is shared under the creative commons doesn’t mean you can use it as you wish. Please try to contact the original creator about redistributing their content yourself and respect their wishes when you receive an answer!
P.S There’s no such thing as copyleft! However, it usually means the work is available for use under creative commons. Please make sure with the original creator whether or not you can use it if you’re not sure!