Here's some Super Mario 64 Beta screenshots. From the third and last Beta version, shown in various Nintendo Power issues that came close to the N64's release.
One shot shown on the back of the Super Mario 64 box. This is, obviously, from the mirror room. Nearly identical to the final version, but the "reflection" doesn't show any paintings. It's possible that the side Mario is on (Not his "reflection") doesn't have paintings either.
Another shot shown on the back of the Mario 64 box, from Bob-Omb Battlefield. Nothing different here, other than the HUD. Also, usually you can't see the black balls in the distance going down the huge white hill until you're beside the third ball (The one closest to the ball going down the hill).