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The negative has been flipped. usually from side to side. Also, if it was moving picture, then the technique is to have back projection, where the movie is projected onto a screen, then recorded from the opposite side.
Many times, you will see this on movies that have titles or letters on vehicles, aircraft, etc. I was watching an episode of "Ice Pilots, NWT" a couple of days ago, and the Canadian Registration letters on the civil aircraft were backwards.
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