There's another way to use computers to help with voting.
Have Ballots with a unique identifier. People come to a polling station, get a ballot, fill in their vote.
The ballot goes through a scanner to tally the vote, and then goes into a standard vote bin.
At the end of voting, you cross-check a random sample (both ways) and check the total number of votes matches between the scanner and bin.
If all goes well, scanner results get electronically combined. If the sampling shows an error, count by hand.
One extra addition. Your ballot is filled out by a separate printer. This ensures proper readability at the scanner, and allows placing the unique ID after someone gave you the ballot (to keep your vote secret). Any tampering with non-unique IDs is detectable by the random sampling.
IDs on ballots don't make sense. You cannot know your ID without breaking a requirement for good free voting systems: It shall not be possible to prove to others how you voted. This is to prevent forcing or purchasing votes.
If you place the ID after the ballot is handed out (by a printer that is also used to fill in the ballot). Then this systems still doesn't allow proving of votes.
The ID here is meant to identify a ballot, not a voter. It should probably be something like a UUID. The aim of this system is to allow cross-checking between the scanner and the physical ballots.
I got that, but you can still kind of prove it. Your know your ID + your-vote. This is likely the only valid ID+vote combination you can know before results are counted. That's when I'd "ask" you and late verify it.
If you want to verify the machine is working, just put the ballot in the standard bin and add those IDs in the counting phase. That seems fine in principle and make it easy to check the tech is working as intended. You'd end up with having list of all individual votes available, maybe even to the public. I'd be worried about people throwing statistical algorithms at that. You better also find a near perfect method to randomize order...
Have Ballots with a unique identifier. People come to a polling station, get a ballot, fill in their vote.
The ballot goes through a scanner to tally the vote, and then goes into a standard vote bin.
At the end of voting, you cross-check a random sample (both ways) and check the total number of votes matches between the scanner and bin.
If all goes well, scanner results get electronically combined. If the sampling shows an error, count by hand.
One extra addition. Your ballot is filled out by a separate printer. This ensures proper readability at the scanner, and allows placing the unique ID after someone gave you the ballot (to keep your vote secret). Any tampering with non-unique IDs is detectable by the random sampling.