On March 29, the Instagram user dickrichter posted an image of a 2010 work by the artist Ryan Sullivan with the comment, “R.S. 2010.” By following up with Dick Richter via email, you could discover that the work was for sale for $120,000.

“Dick Richter Gallery” is a contemporary art gallery working the secondary market solely through an iPhone. It even has a motto: “Here @DR everything is available. We don’t represent artists just a quality of life. Thank you.”

“Its [sic] democracy for the artworld,” “Dick Richter” wrote in an email. He would only speak of his Instagram activities on the condition that we withhold his identity. “Its [sic] an all access pass in a world where some people think you still have to pay to be a vip.”

Even as dealers begin to question the traditional business model of a white-box gallery—with all its overhead costs on top of the continual struggle of midsize businesses against the global enterprises of the wealthiest galleries—Mr. Richter still must maintain a pseudonym. Dealing on Instagram is frowned upon, the equivalent of emailing 300 people and saying you have a Ryan Sullivan for sale and putting it up for grabs. (That’s called burning a painting, a dubious sales practice that’s seen, at best, as tacky.) Five days after Mr. Richter posted the Ryan Sullivan, the L.A.-based collector and adviser Nino Mier commented on the photo, “Rudolf Stingel. Oh wait. No. Knock off artist Ryan Sullivan,” to which Mr. Richter responded, “no opinions here just selling what the people want.” Then the artist and consultant Esteban Schimpf chimed in: “opinions would probably be best.”

An Instagram art dealer was inescapable. With the rise of e-commerce sites like Artsy and Artspace, buying and selling art online has become not only accepted but normal.

“Five years ago, we were all amazed that Jerry Saltz had 5,000 followers on Facebook, which doesn’t seem like a very large number now,” said the dealer Gavin Brown. “Instagram appeals to people on a much more fundamental basis. Photography seems to be taking its proper place as a form of language. You have these emoticons, which are the new hieroglyphics.”

Social media has become a big concern for the art world, and more recently, in the art market. The Art Dealers Association of America has devoted the next installment in its Collectors’ Forum panel discussion series, on May 2 at New York’s Galerie Lelong, to “Social Media and the Arts: The Value of Tweets, Tumbles and ‘Likes.’” As photographs of work proliferate, the legal landscape also must keep up. Organizations like the nonprofit Artists Rights Society are forced to issue numerous takedown notices, according to Adrienne Fields, the associate counsel at ARS. Instagram is now the social media network of choice for the art world, which, Jerry Saltz’s fan base notwithstanding, mostly skipped Facebook and, aside from a few highly active personalities, has avoided Twitter altogether.

Instagram is uniquely suited to the art world because, in the words of Mr. Brown, “Everyone is looking at what everyone else is looking at. I look at the photos, and I look at who’s Liked which of these photos, and you start to realize your fellow members of the hive, what they want to see from you. It’s a kind of averaging effect.”

For dealers, it’s quite possibly the easiest way of selling art—several sources mentioned stirring up interest from collectors accidentally through casually posting images of their back rooms. (Mr. Brown, who prefers to just let the random stream of images “all come at you,” does not use Instagram this way, though he did try to sell a Jeremy Deller print on Tumblr. “It didn’t work,” he said.) Art advisers are scheduling studio visits with undiscovered artists through their Instagram accounts. Collectors, too, create de facto advertisements for themselves by showing people what they have. Alberto Mugrabi recently posted a painting that he owns from Warhol’s Marilyn Monroe series with the comment, “It can be your for the price is right at Philips May auction” [sic], sounding a bit like a billionaire Bob Barker working over a naive game-show contestant.

For now, though, most of the art world is reticent about playing the market in this way. It’s not unlike the Facebook account of a college freshman—it’s fine to be caught in the act of being cool, but no one should have a sense that you’re actually working at it.

Instagram was founded by two young Stanford graduates, Kevin Systrom and Mike Krieger, in the fall of 2010 as a “fast, beautiful and fun way to share your photos with friends and family,” according to its website. In April 2012, when it had already racked up 30 million users, Facebook acquired the company for $1 billion. (Not long after that, Instagram implemented the same terms of service as Facebook, reserving the right to sell any uploaded photos to third parties without consent or notification.) The service is free and available to anyone with an iPhone. It was only a matter of time before the art world became enamored.

“It’s the immediacy of it,” said the artist Eddie Martinez. “There’s no real commitment. You can just scour the thing. You don’t have to publicly acknowledge that you like something. It’s super voyeuristic.”

Instagram is both manageable and highly passive. For the most part, the art world looks only at the rest of the art world, and so, unlike on other social networking sites, this particular online community remains as insular as the real thing. (It helps that many art worlders’ accounts are private—you have to request admission.)

“It’s not as annoying as Facebook—it doesn’t have all that stuff I don’t care about on it,” said the dealer Zach Feuer, whose gallery’s account, like those of most galleries, is public. “It’s all visual. It’s the network where the gallery has the least number of followers. I can be more casual there, unlike on Facebook or Twitter. It’s 300 people and I know all of them. It feels like pretty direct communication.”

Some of that communication, like so much of what can be found in the depths (and, unfortunately, the shallows) of the Internet, is mere time-killing distraction. Jose Freire of Team Gallery posts pictures of his old concert T-shirts. Mr. Brown recently uploaded a brutal image of some dental work he’d had done. The artist Andrew Kuo, easily the most popular of the art world’s Instagram users, broadcasts a lot of funny pictures of cats. (One visitor to his current show at Marlborough Gallery could be overheard saying, quite earnestly, “It’s good, but I wish it was more like his Instagram.”)

But the practical uses have started to seep in. Mr. Feuer said he doesn’t make direct sales using Instagram, but Eleanor Cayre, a consultant and curator, recently uploaded a photo of a piece in Mr. Feuer’s back room and he was contacted by a collector he’d never heard of before. He also said he stumbled upon a painter with whom he did a studio visit in Texas years ago and ended up looking more deeply into her work.

“It doesn’t cause sales for me,” he said, “and if it did, I would have to be more cautious and take it seriously. Right now it’s pretty great. I’m sure it will be gone in six months.”

Ms. Cayre said she uses Instagram to look at art fairs she can’t make it to in person. (She recently bought a work she had been looking for from an art fair she didn’t attend after seeing it posted on Instagram. “I don’t know how I would have known it was being offered if I didn’t see it in the background of someone’s picture,” she said.)

“I like following collectors,” she said, “to see how people are living with their things. Some people don’t use it like that. I once put a picture of a wall in my house—but it’s not something you can do every day. ‘Look what I have.’” But, she said, “I’m in the galleries so often and I see so much of this work in person, it’s not like I could fall in love with a work on Instagram.”

Museums have caught on, though. The Museum of Modern Art’s account, which has almost 150,000 followers, does several posts a week, each of a different artwork in the museum’s permanent collection. The posts invariably get a few thousand Likes and a couple dozen comments.

“It’s almost like a coffee table book with very little text,” said Lindsay Pollock, the editor of Art in America magazine, which recently started doing an Instagram post a day to promote its art reviews (it was inspired by MoMA). “It’s also a popularity contest. I was at a panel and someone from the Tate was talking about how people come to museums and take pictures of themselves in front of an artwork, instead of looking at an artwork. It’s supposed to be a trophy—like, ‘I was here.’ I thought that was fascinating. Museums are trying to grapple with this. In a way, how do you police it? Everywhere you go, people are taking pictures.”

Even if most gallery owners aren’t selling works directly through Instagram, people are starting to make attempts, and iPhone dealing is a new reality to grapple with.

Nino Mier, the collector and adviser, is a prolific Instagrammer. (“I’m obsessed with it,” he said.) He uses his account as a kind of open forum to test his followers’ reaction to a work of art. He posts images without any text—the artist is not named. He knows for sure people are interested if they continue to demand the name of the artist. (“I also post pictures of my dog,” he said.) Sometimes he’ll post an image of an artwork he is trying to decide whether to purchase. Other times, he’ll generate interest around a lesser-known artist. In some instances, this artist’s work is in his personal collection.

Take, for example, the artist Secundino Hernández. “No U.S. gallery represents him,” said Mr. Mier. “I was posting pictures of his for two months. People were literally asking me at openings when they saw me, ‘Who is this guy? I need to know who that guy is.’ And I didn’t tell them, because I wanted to gauge interest in the work and I also wanted to control access to the work, which I have done.”

A few weeks ago, he posted an image of a painting by Dan Rees, who had a show at the Galeria Nuno Centeno in Portugal, which has few ties to U.S. collectors. He tagged the post “New Dan Rees pellet paintings. If you are interested in buying this work, let me know.” The artist Brendan Fowler commented wryly, “2ndary on instagram,” referring to the secondary, or resale, art market. But in an interview, Mr. Mier said that “it was not to sell. It was to promote the show in Portugal. I had no access to that work.”

“I was just talking to a couple advisers the other day,” he continued. “It’s basically 15 of us. And we all know each other and bad-mouth each other and we all convince their clients that they should be working with us. But I feel like if we sat around the table and opened our deck of cards, we’d realize we’re all working with the same inventory. I feel like within that community—I don’t feel like a piece of art should be sold on Instagram.”

If nothing else, it’s proof that the art world is very different than it was even five years ago. Everyone has had to adjust.

The prominent art adviser Thea Westreich Wagner said she had “no idea” what Instagram was, but a member of her staff (the youngest and newest member, in fact) told her it would be useful for the business, so she started an account.

Once the concept was explained to her, she said, “I’m not against it, but I’m a little atavistic. It’s likely to produce a different way of negotiating the art world.” But she said she is still “absolutely committed” to decisions about purchasing an artwork being made only after standing in front of it. When asked about what she thought of an Instagram art gallery, Ms. Westreich Wagner said, “I can’t imagine anybody buying anything that way. It’s a good tool for gathering information—but I don’t know how anybody could buy something that way, particularly on the secondary market, where there are issues of condition and provenance. I don’t know how anybody could do it with any degree of appreciation for what an artwork is.”

Others are more intrigued by the idea.

“What?” the art adviser Alex Marshall said, baffled by even the hypothetical notion of such a business model. “That’s fucking genius!” He let out a big laugh.

“Buy, buy, buy!” he added.