h a l f b a k e r y
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Come to think of it this was probably done some time in the fifties and I've just never heard of it.
I postulate that any letter of the alphabet when viewed through an appropriate lens can be made to appear to be any other letter of the alphabet.
Thus an A could be a V or a Q could be a K or an F so that viewing a message encrypted without the proper series of warping lenses would be unreadable
since even an apostrophe or exclamation mark, heck even a blank space could be made to appear as any letter.
Writing a program which warps pixels to mimic specific lenses on a blown-up image of garbled text would let the recipient decipher the incoming message.