Vincent van Gogh’s “The Starry Night” is one of the bestknown paintings at the Museum of Modern Art. Almost any time of day, a cluster of visitors can be found in front of the 1889 painting, hung on a wall in the fifth-floor painting and sculpture galleries.

On Saturday afternoon, “The Starry Night” attracted its usual crowd of admirers at the museum. For many of them, however, the experience was not what it would have been even five years ago: They were taking pictures with digital cameras or camera phones, and moving on, barely looking at the painting itself.

This is just one example of how the proliferation of digital cameras is changing the museum experience for visitors and the institutions themselves. Museums are packed with visitors who aren’t just looking at art, but photographing it and taking it home, too. For other visitors, the shutterbugs can be an annoyance. For museums, however, the issue is serious: Does the dissemination of copyrighted artwork have financial and legal ramifications?

Some of the museum visitors will post their photos on personal Web sites or to photo-sharing sites such as Flickr.com. Others will print and frame their shots in their homes, instead of purchasing a print at the museum gift shop. The MoMA shop sells reproductions of “The Starry Night” that range between $8.50 and $175, for example, as well as journals, note cards, and sticky-note pads.

The public information officer at the Brooklyn Museum, Sally Williams, said camera-phone use by visitors is a growing problem. “We have seen a great uptick of people in the galleries who are supposedly text messaging,” she said. “Then suddenly we see all of these pictures on Flickr of our special exhibitions. It’s clear that this new technology has made it far easier for people to forgo our camera policy.”

Some New York museums, including the Jewish Museum and the Whitney Museum of American Art, do not allow photography at all. But many — including MoMA, the Metropolitan Museum of Art, and the Brooklyn Museum — have more lenient policies. Visitors may take photographs without using a flash in galleries that house works in the museum’s permanent collection. But they may not take photographs of any kind in galleries that house special collections. “We don’t have permission from lending institutions,” the chief communications officer for the Met, Elyse Topalian, explained. Taking snapshots is legally considered making a copy, and museums cannot authorize the copying of art owned by other institutions.

These policies were developed before the advent of digital cameras and camera phones, however, when cameras were heavier and each snap of the shutter had a cost in film. Now millions of Americans, including the tourists flocking to New York City museums, carry light cameras with virtually limitless free storage capabilities. The cameras are small and silent — perfect for sneaking into special exhibitions.

An attorney and partner at Moses & Singer LLP, Paul Fakler, said the legal responsibilities of museums are murky. Generally, works of art that were created before 1923, such as “The Starry Night,” are not subject to copyright law. For newer works that are covered, there is a distinction between owning a work of art — the physical piece itself — and owning the right to copy it, which is usually held by the artist or his estate. MoMA and the Met do not hold the copyrights to newer works in their permanent collections. Allowing public photography of this work is generally justified as fair use, depending on several factors, including the quality of the image and whether it is for private use.

As long as museums make a good-faith effort to prevent improper use of visitor photographs, Mr. Fakler said, they are unlikely to be held legally responsible. But if visitors are taking high-quality photographs for print purposes — which many high-end digital cameras are capable of — the legal question becomes trickier.

“As a general matter, it would be unlikely to be fair use if a museum visitor were taking photos and printing them out as posters,” Mr. Fakler said. “It would pretty directly harm the market.”

Indeed, the photo-sharing Web site Flickr.com features a wide collection of surreptitiously snapped images from special exhibitions. At the Brooklyn Museum, Ms. Williams said, the recently closed Annie Leibovitz photography show was particularly popular. From the Met, the Web site has photographs of “Nan Kempner: American Chic,” “Glitter and Doom: German Portraits from the 1920s,” and the recently closed “Sean Scully: Wall of Light.”

MoMA special exhibitions on Flickr include “Manet and the Execution of Maximilian,” the 2006 exhibit “Edvard Munch: The Modern Life of the Soul,” and the recently closed “Brice Marden: A Retrospective of Paintings and Drawings.”

Many of the MoMA photographs are included in “Impressions of MoMA,” a Flickr-based project of brothers Travis and Brady Hammond. Their intention with “iMo-MA” is to gather snapshots of every piece of art in MoMA’s collection — 150,000 items, not including film and video work. “With mobile phones, everyone is an artist,” Brady Hammond said. “It would be the ultimate postmodern gallery.”

The project began last August, and has so far amassed about 11,000 photographs taken by 2,000 contributors, who post their snapshots to a page on Flickr. Brady Hammond, who works as an ESL teacher in Boston, said he does not know if MoMA is aware of iMoMA. “We’re kind of concerned that the first thing we hear will be a cease and desist,” he said. “But I imagine that they would respect the effort we’re making. Our ultimate dream would be to have them say, This is a good idea. And even maybe have a little kiosk in the museum. Who wouldn’t want to go to a world famous art gallery and see their work on display?”

A representative for MoMA declined to discuss the museum’s policy on the record.

Ms. Topalian was quick to say she had not noticed an increase in digital camera use at the Met. “We have such a huge influx of tourists,” she said. “We’re a big destination, with 4.5 million visitors a year. Photography has always been a part of that.”

Steve Scannell, visiting the Met on Saturday, was standing back to take a digital photograph of Gaston Lachaise’s 1932 bronze sculpture “Standing Woman.” He said he took between 50 and 60 high-resolution digital photographs at the museum that day. He said he was primarily shooting sculptures, and that he would show the pictures to his son, who is studying sculpture at the University of Kansas. “But if there are some of the paintings we really like,” he added, “we might blow them up, print them up at 11 by 17 [inches] and enjoy them in our home.”

Jaclyn Bradley, who was visiting New York from Cleveland, Ohio, was strolling through MoMA on Saturday. “To download these things would be a couple of dollars,” she said of the works she had shot with her camera phone. “It’s cool to have them, if you like art, just to look at.”

Her cell phone’s screensaver was “The Starry Night,” snapped just minutes before.