The correct answer to this open question is the following.
The voter i.d. policy that would result in the freest and fair electoral process would be to issue a National Credential for Elections, that its only purpose would be to vote during elections. The best example could be the case of Mexico's vote credential.
The National Electoral Institute has issued the "electoral credential" with many security measures, including a chip, that makes it so difficult to falsify. You can do all the paperwork on the web page of the official site and you just have to go one time to the electoral office in your neighborhood to have your photograph taken and your fingerprints taken, And that's it. It is a 10-year credential. And after you vote in one election, officials punch your card in the date of the election that appears in the credential so you can use it only once in that election and prevent frauds.