Zapruder (Odds & Ends)
(This stuff is all related to an argument that the headshot could be from the front.)
The 'Explosion' 1
The image above shows Jackie's face, in Z312 & then 313.
The 'Explosion' 2
The top picture of this pair is a 'shadow enhanced' b&w version of 313, giving a clear idea of the extent of the avulsion of matter.
The 'Imaginary Forward Motion'
This (above) shows the forward motion of the head after the shot, and clearly also demonstrates that the blur in 313 is in fact to the left. Thus it can have no impact on the percieved forward motion of the head. (This graphic is cropped at the right of the blur simply because I made the picture for other purposes, not to demonstrate this, and didn't in fact notice the effect until after the graphic was substantially finished. An examination of Z313 will show that the full extent of the blur is in fact shown here.)
More 'Imaginary' Forward Motion
Just to be sure we are not seeing "motion blur", here's z312 and then 314.....(above) a frame which is very little more blurred than 312 itself. The direction of motion of the head is perpendicular to the direction of blurring. (This can be seen by examining the highlight on the doorhandle, for instance.)
Also note the appearance of a large highlight low on the seatback, behind JFK. This is of course impossible unless he had bodily shifted/ rotated forwards.