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

There are many images like this, where someone standing on the south side of Elm shoots towards the street and captures the downward slant of the road.

So, why don't we see the downward slant as well in the Moorman photo?

It's because of what the Moorman photo is: a cookie-cutout of a larger photo taken by Babushka Lady. And BL shot at a diagonal. And what happens when you shoot at a diagonal? You capture a larger field. 

So, when I say that the Moorman photo was taken by Babushka Lady, I don't mean that it is the entire image that BL took. It's a crop of it. And once you start cropping, you lose your bearing to the ground, and you can turn the crop any which way you want.