Imitating League's art style.

I've seen dozens of photos like this one, where an artist has done their own render of what a skin would look like in-game so perfectly that you could swear that they are actual in-game screenshots. Does anyone have any clue as to how so many people have managed to have it work so well. Has there been some kind of video released by Riot demonstrating techniques with which the art is made, or is there some kind of subreddit/community of people who do exactly this kind of stuff that I just don't know about?