Justin Bieber allegedly moons Lil Za on Instagram

Justin Bieber is snowboarding now with his buddies.

He posted a few photos over the weekend but also one that "mooned" Lil Za with the caption: "@LilZa u a** leep????"

No confirmation yet if this is Justin or not -- though we've seen Justin Bieber's ass before, so this could be normal for him.

I could do a forensic picture analysis, but I don't want to.