> But you could also hide a camera in the booth, which is easier.
It is also easier to check whether there is a camera in the booth.
Is it? Cameras can be really small.
You can see it this way: if you can time people voting, you can hide the camera anywhere in the voting room. Checking the booth is always going to be easier than checking the room.
There is also the issue of voters selling their vote. It's pretty easy for them to wear a tracker that tells you when they were in the booth. On the other hand, with paper ballots, the buyer has no way to check the vote, since market ballots are null.
You have a paper trail, it anonymous, and it's pretty easy to understand.
I guess if you modified the firmware on the scanner to disclose the vote counters continuously, and the worker at the end knew me by sight (the worker I showed my I'd to is on the other end of the room) you could find my vote. But you could also hide a camera in the booth, which is easier.