It is there in the new 3-D version of “Titanic,” as it was in James Cameron’s original film: a modified version of Picasso’s painting “Les Demoiselles d’Avignon” aboard the ship as it sinks.


Of course that 1907 masterpiece was never lost to the North Atlantic. It has been at the Museum of Modern Art for decades — which is precisely the reason the Picasso estate, which owns the copyright to the image, refused Mr. Cameron’s original request to include it in his 1997 movie.


But Mr. Cameron used it anyway.


After Artists Rights Society, a company that guards intellectual property rights for more than 50,000 visual artists or their estates, including Picasso’s, complained, however, Mr. Cameron agreed to pay a fee for the right to use the image.


With the rerelease of “Titanic,” the society wants Mr. Cameron to pay again, asserting that the 3-D version is a new work, not covered under the previous agreement.


“I don’t expect we’ll have any difficulty,” said Theodore Feder, president of the society, who contacted Mr. Cameron last week.


Filmmakers are not the only ones who sometimes run afoul of artists’ copyright law. In recent weeks Google Art Project, which just expanded its online collection of images to more than 30,000 works from 151 museums, agreed, because of copyright challenges, to remove 21 images it had posted.


Artists’ copyright is frequently misunderstood. Even if a painting (or drawing or photograph) has been sold to a collector or a museum, in general, the artist or his heirs retain control of the original image for 70 years after the artist’s death.


Think of a novel. You may own a book, but you don’t own the writer’s words; they remain the intellectual property of the author for a time.


So while MoMA owns the actual canvas of “Les Demoiselles,” the family of Picasso, who died in 1973, still owns the image. And under existing law, the estate will continue to own the copyright until 2043.


If someone wants to reproduce the painting — on a Web site, a calendar, a T-shirt, or in a film — it is the estate that must give its permission, not the museum. That is why, despite the expansion, Google Art Project still does not contain a single Picasso.


Indeed, few 20th-century artists are included in the project’s digital collection because copyright owners have not yet given permission. “We don’t want to prevent Google from showing the work, but they won’t enter into negotiations with us,” Mr. Feder said.


The Art Project’s position is that it is the responsibility of each museum to get copyright permission. “Google is placing the burden and onus on the museum, which is unfair to them and unfair to the artists,” Mr. Feder said.


Robert Panzer, executive director of VAGA, a second company that represents the copyright interests of artists, said that Google was legally responsible for securing the permissions. “It’s a game that they should try to make it someone else’s responsibility,” said Mr. Panzer, whose group represents more than 7,000 artists worldwide.


The Toledo Museum of Art recently asked the Google Art Project to remove “Dancer Resting” (1940), by Henri Matisse, as well as 20 other images from its collection that were posted but are still under copyright.


“There had been some confusion on all sides,” said Kelly Garrow, director of communications for the Toledo museum. “We want those works on the Art Project, but there needs to be some type of agreement to make that happen.”


Mr. Panzer, whose group is currently doing a review of all the work posted on the Art Project, said the underlying question was what Google’s business plans are in the long term: “We have to make sure that the artists’ interests from an aesthetic point of view and a commercial point of view are protected.”