Free the Nipple has been a cause for years, and the hashtag on Instagram now aggregates more than four million posts. Leah, 41, has been communicating directly with representatives from Facebook for about a year and a half about her concerns over how their policy affects artists like her. So the company decided it was time for a meeting.

Last month it hosted about two dozen artists and anticensorship activists at its offices in Lower Manhattan for a five-hour discussion with the company about Instagram’s policing of nudity in their work. The company representatives listened, but gave no signs of budging, according to several people who attended. The company told them that it was just keeping within the bounds of social propriety: If you walked down the street in New York, one employee explained, you wouldn’t see exposed female nipples on advertisements.

One of those who attended, Micol Hebron, 47, an interdisciplinary artist in Los Angeles (Instagram paid for her travel), snapped a topless selfie outside the building and tried to post it after the meeting. Almost immediately, her Instagram account was shut down.

Several years ago, after Facebook took down a topless photo of Hebron from an art exhibition about breast cancer awareness, she created what she calls a male nipple pasty — a circular cutout of a man’s nipple that a woman can copy and can stick on her own nipples.

As Hebron’s pasty cleverly pointed out, Instagram’s ban does not extend to male nipples. In the real world, the female breast has had some success on the equal-rights front.

In February, a federal appeals court in Denver decided against Fort Collins, Colo., which sought to uphold an ordinance banning women from going topless in public. In New York, a 1992 State Court of Appeals decision established women’s right to go topless in public for noncommercial reasons. But decisions elsewhere have let similar laws stay on the books because, unlike male chests, female chests were considered to be an “erogenous zone.”