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This question arose when a friend noticed that some scenes in the first episode of The Planets had been filmed in the desert on Lanzarote - I had assumed they were computer-generated.
But I think the scheme is impractical. Too many symbols would be needed to cover all circumstances e.g. is a film of an actor playing Elizabeth I real?
Even speed can't be easily shown. When Hermione turns back the clock, she and Harry act in real time (X1) in the foreground, while the background recedes (X-500, say).