If we stand three feet from a large mirror on the wall, we see our reflection three feet from our eyes in the plate glass and we see it at the same time six feet from our eye behind the glass.

Both localizations take hold of our mind and produce a peculiar interference.

We all have learned to ignore it, but characteristic illusions remain which indicate the reality of this doubleness.
In the case of the picture on the screen this conflict is much stronger.
_We certainly see the depth, and yet we cannot accept it._ There is too much which inhibits belief and interferes with the interpretation of the people and landscape before us as truly plastic.

They are surely not simply pictures.

The persons can move toward us and away from us, and the river flows into a distant valley.