Yeah, a few times. Several years ago I did this piece of Avatar the Last Airbender fanart of Aang in his Avatar State with all the elements swirling around him like in the finale...

It got stupidly popular, and now I guess people just assume it's a legit piece of licensed art from the show, because people keep using it in memes and turning it into wallpapers and using it as their SoundCloud album covers. And there have definitely been people who traced it (usually badly) or recolored it (also badly) and tried to pass it off as their own.