Official art tag usage for fangames

With the rise of fangames such as Touhou Lost Word and Fate/Empire of Dirt, what should their artworks be tagged as?
By definition they're not official art of the main series, since they're fanworks, but they're official art of their own game.
Should a new tag be made? Something like Fanwork Official Art?

game cg? There's gotta be a more concise tag to apply to these works.

tapnek said:

game cg? There's gotta be a more concise tag to apply to these works.

Game CG is for artworks in games, it doesn't matter whether official or unofficial. I was trying to look for a way to differentiate between official and unofficial content.