FYI: Regardless of other states' stance, it remains illegal in NY.

Donald Trump's son, Eric Trump, tweeted out a picture of his own vote and then deleted it, technically a violation of New York state law. Additionally, both Trump men were captured in photos or video violating the principle of ballot secrecy by seemingly checking out their wives’ ballots.

As Ars reported last week, a federal judge in New York rejected plaintiffs’ attempts to halt an existing state and New York City law that bans the practice of a ballot selfie. The judge wrestled with balancing First Amendment free speech rights against the public policy interest in keeping a secret ballot so that voting is not unduly influenced.
“The absence of recent evidence of this kind of voter bribery or intimidation does not mean that the motivation to engage in such conduct no longer exists,” US District Judge P. Kevin Castel wrote. “Rather, it is consistent with the continued effectiveness of the New York statute.”

The judge also found it a bit strange that the lawsuit was brought just 13 days before the November 8 election, “even though the statute has been on the books longer than anyone has been alive.” The judge also noted that smartphone cameras, and therefore the possibility of a ballot selfie, “have been prevalent since 2007.”

Ballot selfies are legal in some states, including Washington, Oregon, Louisiana, and the District of Columbia. And the issue has come up earlier this election season with high-profile ballot selfies coming from the likes of Justin Timberlake (or this reporter). While some states, like New Hampshire, have recently overturned laws preventing the practice, New York still bars such activity.