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

David Von Pein offers this image from another photo in that set as a justification for what we see in the disputed photo.

In this case, Jackie is turned to her left, and we can see her left upper arm. Let's compare it to the other one.

On the right, we see, conspicuously, the left shoulder, the left upper arm, and the left forearm. All is accounted for. I don't have any problems with that image. Note that Jackie is gazing to the left. On the right, she appears to be gazing straight ahead. Also observe how low her forearm is on the right. That's because her arm is going down, and the elbow is at a low point. But, look how high her forearm is on the left. Her forearm is as high as her right shoulder. 

So, I drew a line from the seam of her shoulder to her forearm to show you how high her forearm is. So, with her forearm being that high, how does it leave room for an upper arm bone? Where do you squeeze it in?

In the image below, the white vector shows you the source of the whole movement: her shoulder. That's where it starts. So, the upper arm connects her shoulder blade with her forearm. So, the white vector is showing the path her upper arm has to take. It's got to get to the forearm, right? And it's solid and inflexible, right? And the yellow line shows the path that her forearm is taking.

So now, let's compare to the valid photo again.

I have them reversed this time, but the one on the left is valid. Everything is accounted for. The one on the right is not valid because everything is not accounted for. Her upper arm is not accounted for. The other image helps clarify it.