How to prove photography to a blind man

I knew what he was getting at. We had been discussing psychics. He was a firm believer in psychic powers, had had psychic experiences, and regularly visited a psychic. His point was, since I had not experienced psychic powers, I would never be able to believe in what he  “knew” to be true. You could never prove to a blind man that photography exists, and likewise no one would ever be able to demonstrate to me that psychic powers were real.

It took me about ten seconds to think of a way to show he was wrong. This is what I said. Give the blind man a camera, a tripod and a remote shutter release. (Ideally the camera is a Polaroid, or a digital with an instant picture facility.) Everyone leaves the room but the blind man. He takes a picture of himself, and holds up a number of fingers (1 to 5) at random. The sighted person comes back into the room, looks at the picture and says “you were holding up X fingers.” If he gets the right number, and continues to do so every time this experiment is performed, the blind man will eventually conclude that photography is real. Technically, he will conclude the hypothesis that “a camera can record a visual image,” might be true.

Skeptico: How do you prove photography to a blind man?

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