Ok, straight off, I'm not a conspiracy theorist so I'm not sure I should be posting this at all, but the source is a respectable MSM news magazine.
US News & World Report has a couple of short pieces (one and two) about possible tampering involving the Zapruder film of the assassination of JFK. Links to scanned images are on the second of the two pages. Comparison of the images allegedly show discrepencies in the color of shoes, which is why I thought this might be of professional interest. Please note that I have not studied these in detail and am not supporting or refuting any allegations.
(Image Source: US News & World Report)