The states that have voter ids do not require proof of citizenship. Most states now require some form of id. If you forced every voter to produce a picture id that proves citizenship, you stop mail in voting, restrict registration, etc. Maybe 90% of voter would comply because they take voting seriously. For the rest of the voters, they are not going to dig up a birth certificate, go to a voter registration office to get certified to vote and stand in line at a poling place to vote. These are people who have other priorities, they don't believe their vote will change anything. I think we have millions of voters like this. They vote because it's easy and studies confirmed it. The easier we may voting the better the turnout.