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The problem with paper is vote buying.
If you give a receipt that the voter can carry out the door it will be used as proof for liquor, drugs or money.
After many years in the computer business I advocate paper ballots. Count them by hand or OCR them but give every voter a piece of paper on which to cast their vote. Simple, cheap and verifiable.
The tricky part is to be sure each voter turns in the ballot they were given by a poll worker so no pre-marked ballots find their way into the system.
The old liquor, drugs or money method was to send in a voter with a pre-marked ballot and give them their goods in exchange for the blank ballot they were given inside. Not a good way to run an fair election...