A ballot selfie -- like a campaign button -- is a way to express support for or against a cause or a candidate. And because it is tangible proof of how a voter has voted, a ballot selfie is a uniquely powerful form of political expression. It proves that the voter's stated political convictions are not just idle talk. Not only that, but ballot selfies and other digital expressions of civic engagement encourage others to vote -- particularly younger voters who have historically low turnout rates. Ballot selfies are thus all at once deeply personal and virtuously public expressions.

And they're the sort of expressions that the State cannot categorically ban without violating the First Amendment.