Photo via Sebastiaan ter Burg (CC-BY-SA)
It might seem completely reasonable to you to want to take a selfie while at the voting booth. Just know that if you do, the next picture of you might be in a courtroom.
For voters in the state of New York, selfies and pictures that are taken from inside the voting booth are illegal. State law dictates that any person who "makes or keeps any memorandum of anything occurring within the booth, or directly or indirectly, reveals to another the name of any candidate voted for by such voter; or shows his ballot after it is prepared for voting, to any person so as to reveal the contents" is guilty of a misdemeanor.
The law also prohibits pictures of completed ballots, which is primarily to thwart vote buying efforts. Despite what is inferred by widespread voter ID laws, voter fraud is incredibly rare, but selling votes is among the most common forms of it. The purchase requires a verification process—which is why it primarily takes place via absentee ballots—and the ballot selfie could serve that purpose on voting day.
Bans on photography from the voting booth could be on their way out; in 2014, a federal court struck down New Hampshire's law that banned people from taking pictures with marked ballots, finding it to be a violation of free speech. The ruling may open the doors for a flood of ballot selfies on Facebook in future elections.
It might not be such a bad thing, either; research found that posts on Facebook encourage and increase voter turnout. While Facebook's own "get out and vote" messages don't have much of an impact according to the study, users who saw photos of friends participating in the electoral process were more likely to vote.
For the time being, though, the ballot selfie is still prohibited in New York, so it's probably best to not take one. Frankly, there are tons of situations in which you shouldn't take a selfie, it's just this instance happens to be illegal rather than just ill-advised. Just take your picture with the "I Voted" sticker and call it a day.