>It's unclear to me why the wall would need to be "blank" The initial state of the wall (before people are introduced) should be known. With a solid color wal

>It's unclear to me why the wall would need to be "blank" The initial state of the wall (before people are introduced) should be known. With a solid color wall you can find shadows of people, objects, etc. But with a wall with objects on it, you need an image of it before the room was filled, in order to interpret the shadows. (From a machine standpoint. As humans we can process out the art or whatever is on the wall)