Has to be documented facial recognition. Mag strips can be altered. IDs can be faked. Data on IDs and on mag strips can be faked. Put a person’s face against a facial recognition program, and you put fear of getting caught on the table, federal offense sort of stuff.
Purple fingers won’t work here. It would be just one election cycle and someone will find a solution or agent to remove the ink.
You could use fingerprinting too. The technology exists to do it - don’t let anybody tell you otherwise. You register to vote with a fingerprint, then you have to use a fingerprint to get a ballot. It could be set up so that you get a paper trail of your ballot and can register that information at a point outside the polling place also - then we could actually check against claimed voter rolls as well.
The bottom line here is that there has to be something better than what we do now - there are no checks and balances to the process...