A system that was used in some counties in California a few years ago used a paper ballot that was marked by the voter, and then fed by the voter into an optica

A system that was used in some counties in California a few years ago used a paper ballot that was marked by the voter, and then fed by the voter into an optical scanner (made by Eagle, IIRC) which either successfully scanned the ballot, xor returned it to the voter in cases like: extraneous marks, votes for too many candidates in a multi-seat poll (like 4 candidates marked for 3 city council seats among 11 candidates) and similar. The voter could exchange their improperly marked ballot for a fresh blank ballot and start over. The net effect was that all ballots scanned by the voter needed no further inspection - an effect that is sadly lost in vote-by-mail.