I think John asks a good question, and it's one I have pondered myself. With appropriate computer analysis, I think that there may be opportunities to at least prove differences and discrepancies in the background, missing frames, proof of magnification, etc. With modeling and trending, you could put together some views of what was occurring to the President as he passed out of sight behind the Stemmons Freeway sign, but whatever valuable 'other' detail was removed can't truly be restored in this fashion.
I recently purchased "Image of an Assassin" and was greatly disappointed. I also stood in Dealey plaza last week Friday [first time there] and video taped Elm Street from 'Zapruder's pedestal.' What I noted was, in rewatching the "Image of an Assassin" was that, unless Zapruder was completely blind [which I have seen some substantiated claims regarding his glasses and his ability to even film the scene], why couldn't he keep his main character, The President of the Unites States, whom he had gone to some length to film, in the center of his shot? As the limo begins panning down further and further into the edge of the film, you have to wonder what the heck he was doing [unless of course someone else had reshot his film through his own camera, in possession of the FBI at that time, and magnified the top half of the scenes].
Jack White has a great analysis of the Z-Film in James H. Fetzers, "Murder in Dealey Plaza," Catfeet Press, Chicago, Copyright 2000. His photographic analyses of many of the frames go beyond his response here - and also give information and comparisons of the Z-film to the Moorman Polaroid, the Nix film, the Oliver film, etc.
But this is not why I chose to reply to John's question. I would like to answer John's question with another question - which I believe would resolve the issue, if at all feasible. If you can accept the veracity of claims which have been made substantiating the existence of an unaltered Z-film [turn on Elm, Moorman's position, no missing frames, halo of material behind JFK's head, head moving forward, pick-up man visible, Life photos, etc.], how would we go about getting one?
2 are at the Archives - SS#1 and SS#2, there are apparent differences even between these 2 versions [leader, frames, etc.,] as covered by David Mantik, in the same book referenced above, "Murder in Dealey Plaza."
Here's the real reason I am responding. It bothers me greatly that H.L. Hunt, the oilman with an office on Dealey Plaza, who has been implicated in the conspiracy, had motive based upon Kennedy's threat to end the "Oil Depletion Allowance," was a Texan of some political influence, an associated of LBJ, was a part of the right wing, plus the 'Torbitt Document" which states that Hoover had his men remove Hunt and his family at 12:30pm, 11/22/63 and fly them to a hotel in NY
http://www.parascope.com/articles/1196/torbitt.htm --
Can't find the reference at the moment, but I understand Hunt managed to obtain his own personal copy! Possibly at odds with the agreement signed by Zapruder in which copying was legally limited to a set number.
Although it's amazing that this man could have ended up with a copy of the Z-film - potentially before even Life magazine, how would we go about getting it? If fact, has anyone considered pursuit of this early edition copy?