Oswald in the doorway: the blog of the Oswald Innocence Campaign, by Ralph Cinque

Backes, the point is that he drew this just by looking at the Moorman photo and not being told anything else. The point is that he located the photographer. The point is that he could look at the photo and see that it was not taken by someone who was facing Elm Street perpendicularly, as Mary Moorman was. 

And that's where the Physics comes in. He knew that anyone facing Elm Street perpendicularly as Mary Moorman was would not have gotten these two non-parallel lines: 

You are an idiot, Backes, and you're not fit to empty this professor's trash.