Jonathan, on the surface your reasoning seems (and is sound). My question would be, How many of these photos/films have been "passed through" various agencies (CIA ["Time-Life"]/FBI/HSCA), examined,studied or in other ways and out of the hands of the owners. I think all or virtually all were. If the CIA was involved (I think they were), those at the top of the conspiracy to kill would be the same ones who could oversee the gathering and censorship of the visual evidence. Those not involved would/could be manipulated by use of the "state secrecy" and internal classification. After all, you wouldn't want to start WWIII by revealing something told to you by the top members of the intelligence agencies (especially in the 1960's/cold war era). Once changes/edits/splices, etc. are in place you can't go back to the originals and no one has anything more than a memory that the photo/film somehow looks different than it did originally. I have seen, heard or read many accounts of the people having made the photos or films saying their memory of what they sent in is slightly different from what was returned. Also, many were simply returned "damaged" by those darn professionals that handled the materials while in "official hands". I feel this accounts for possible alteration in the (Keep It Simple Stupid/Ocams Razor) method. Just my opinion though.