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

This third drawing by the professor is much more complex than the first two. But, what he's saying here, in physics display, is that the line of the car should be parallel with the bottom of the picture- if Mary took the picture, facing Elm Street squarely, as claimed.

But, the observation that it's based on is simply this, where you can plainly see that the line of the limo is NOT parallel with the bottom of the picture. It proves that the picture was taken on a diagonal.