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In reply to the discussion: Cold Case: JFK – NOVA program now online [View all]William Seger
(12,411 posts)He is simply wrong, but you have credulously accepted it because of your own confirmation bias.
Yes, frame 313 is blurred by camera motion, but that doesn't mean that you can assume that any "horizontal elongation" is a result of that motion. The forward snap cannot be explained by the camera motion for a simple reason that he completely missed, but which was already taken into account in the gif that was posted (and many others):

Notice that the white lines at Connally's head, Jackie's hat and left arm, and the door handle are all set to be on the right end of those motion blurs, such that all the blur of those objects is toward the left. It isn't possible to say from just these two frames whether the right end of those blurs the beginning or the end of the exposure for frame 313, but we can say one thing: No motion blur caused by camera motion can be towards the right of where an object is in frame 312; all the camera motion blur is towards the left.
Now think about what that means for the hypothesis that the forward head snap is an illusion caused by the motion blur. (No, seriously, think about it before replying.)