“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.”

Amit Sood, head of the Google Art Project, said it had decided early on to focus on its partnerships with museums. “We have been approached by commercial organizations who wanted to sell us content, but we chose to work directly with the museums,” Mr. Sood said. “We believe they are in the best position to assess rights status and we are happy to work with them to address any concerns.”Groups representing authors and publishers have been trying for years to come to an agreement with Google over its plan to digitize every book published. But after a federal judge threw out a proposed settlement in 2011, citing copyright and monopoly concerns, no agreement is in sight.

Raymond Dowd, a lawyer who has represented both sides on copyright questions, said of the Google Art Project: “Every artist is going to have a different view of it. Some will think it’s the greatest thing in the world and others will be horrified, just as the writers were, and just as musicians have been.”

Copyright law covers everything from reproductions in books to those used on keychains. “We try to acquire as much information as we can about a project, and then we go to the estate,” Mr. Feder of Artists Right Society explained. His organization, like VAGA, takes a percentage of the fee, which varies depending on the use.

Sometimes artists or estates want input. In the 2011 film “Tower Heist,” for example, the estate of Dan Flavin sent an expert to oversee the construction of a Flavin light installation that was recreated on the set.