It's a cat-and-mouse game that the cat usually wins, since the cat has access to artificial intelligence and 15,000 people working around the world to review posts and look for banned material.
"Censoring photography is invalidating it as an art form," said Joanne Leah, a New York City-based photographer who estimates that she has about one post removed every month. "Every time something gets censored, it feels like a punch in the gut."
Since Instagram's ascent as a mainstream, image-centric social media platform, it has effectively turned its users into published photographers. It has also allowed artists, once at the mercy of galleries, to promote their work independently, as long as they abide by certain rules.
There are plenty of risqué images allowed on the site. Photos of women in sheer tops — the shape of their nipples exposed — often stay up, as do some with the nipples craftily covered or altered. But bare nipples on a photograph of a woman are off limits, though Instagram says it makes allowances for users who make it clear that the display of nudity is meant as a form of protest or to raise awareness for a cause. That's why photos of mastectomy scarring and breastfeeding are allowed. (Instagram started allowing photos and videos of breastfeeding in 2014 after pressure from activists.)
The same rules apply on Facebook, which owns Instagram. In defending its policies, the company emphasises its vast global reach: 2.4 billion monthly users on Facebook, and more than 1 billion on Instagram, both in 100 languages.
In an email, Instagram's head of public policy, Karina Newton, said the site wasn't trying to "impose its own value judgment on how nipples should be viewed in society."
"We're trying to reflect the sensitivities of the broad and diverse array of cultures and countries across the world in our policies," Newton said.
Instagram's rationale for drawing a line between photography and other forms of fine art is that the nipples typically belong to living people, and the site cannot know for sure whether the subjects have given consent. Posting a photo of a marble Aphrodite doesn't present the same problem.
Pictures of genitals and "close-ups of fully nude buttocks" are also against the rules, but it's the explicit exclusion of the female nipple that has drawn the fiercest objections.
Rihanna, Miley Cyrus and Chrissy Teigen, who have tens of millions of followers each, have tested the Instagram censors by exposing their nipples in posts that were swiftly taken down by Instagram. But at the forefront of the movement have been artists who have put persistent pressure on Instagram to loosen its restrictions in a way, some of them acknowledge, that would run afoul of social custom.
Free the Nipple has been a cause for years, and the hashtag on Instagram now aggregates more than 4 million posts. Leah, 41, has been communicating directly with Facebook representatives 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 anti-censorship activists at its offices in New York City for a 5-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 called 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 cleverly pointed out with the pasty, 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, Colorado, which sought to uphold an ordinance barring 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."
When it comes to nipples, there are "criteria" to help both human and technological reviewers identify a nipple as male or female, Instagram's Newton said. The criteria include indicators of the person's gender, an Instagram spokeswoman said. But Instagram stresses that the system is imperfect. "There are times that we can't tell — and mistakes may be made," Newton said.
In July, Instagram introduced the option for users to appeal deleted content; before, users could appeal if their account had been deleted but not in response to individual posts having been removed.
As the great democratiser of photography, Instagram has opened up a new chapter of art history. From depictions of the nursing Madonna in 14th-century Italy to Frenchwomen lounging in the nude in 16th-century paintings, bare breasts have long been an artistic preoccupation, the gender studies scholar Marilyn Yalom wrote in the 1997 book "A History of the Breast."
"Though breasts still carry an overload of cultural and sexual expectations, many women hope to see the day when their chests do not have to bear such a burden," Yalom wrote.
What is different about the current era of nude art is that women are often the ones wielding the camera or the paintbrush.
Mona Kuhn, 49, a Brazilian-born photographer, whose work focuses on the human form and often captures nude figures, has had work exhibited at the Louvre and the J. Paul Getty Museum in Los Angeles.
But on Instagram, she said, she has to hold back what she considers some of her most important pieces.
"I cannot promote my work as much as some other person who does landscapes," she said.
Other artists have accepted the reality that they don't have free rein on such a wildly popular, global platform. "No one forced us to use Instagram," said John Yuyi, 28, who uses her own body, with nipples obscured, to make popular Instagram posts about human interaction with technology. "They can say, 'If you don't like our rules, you can find another social media.'"
At Facebook's meeting, some artists pressed the tech employees on the matter of transgender and nonbinary users posting topless images. Is it still a female nipple if the person no longer self-identifies as a female? What if a person's nipples used to be anatomically male, but that person transitioned to being a woman?
Last year, Rain Dove, a gender-nonconforming model with more than 360,000 Instagram followers who uses gender-neutral personal pronouns, engaged in a battle with the platform's censors after posting topless images with breasts exposed. In one video, the model was playing basketball. In another, they were drinking from a gallon of milk, wearing only boxer briefs.
Rain Dove, 30, said in an interview that after Instagram took down two of the topless posts, they repeatedly republished them. They wrote in the caption that because they did not consider themselves female, their nipples weren't female either. In the caption's text, the model threatened to take legal action if Instagram continued to remove their posts, and eventually, the bare-chested images were allowed to stay.
"No one's head exploded," Rain Dove said. "We're all going to be fine!"
Newton said that if Instagram's content reviewers had context signaling that a user identified as a man or nonbinary (for example, if the user states a pronoun preference), nipple exposure was allowed. And if a transgender woman posts an image of exposed nipples, Instagram will remove it.
But Instagram is not showing any signs of relaxing its general ban on female nipples. So artists have begun to factor that into their work, even as #freethenipple lives on.
Amanda Charchian, a commercial and artistic photographer who shoots nudes, often obscures women's nipples with pinpoints of color or a blurring feature. Charchian, 31, is now working on a series that involves the application of paint to photographs of nude women and architecture, and she said that she felt Instagram's restrictions creeping into her artistic process.
"When there's a nipple, I think to myself, 'Should I cover it or not?'" she said. "That's the infiltration of Instagram censorship on my mind and my creative decision-making."
Written by: Julia Jacobs
© 2019 THE NEW YORK TIMES