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Several New York art appraisers, including Kimball Higgs, director of art advisory at Winston Art Group, said the pieces could sell for as much as $800,000.

Keszler said he acquired the pieces from the building and car owners, adding that he receives calls every day from New Yorkers asking him to buy the Banksy that appeared on their property.

Many of the pieces have already been defaced by competing graffiti artists or people who just do not like graffiti, Keszler said, adding that he believes buying the art allows him to protect it from damage.

Not all art enthusiasts shared that view.

"Maybe it's not meant to be saved," said Alexander Madrigale, a street art expert with Doyle Auction House in New York who curated the first street art auction by a U.S. auction house last fall.

"The work appeared in the street because the artists' intention is that it has a life cycle, it has decay, destruction," Madrigale said.

Banksy creates a large amount of artwork expressly for art auctions that is authenticated by an appraisal firm called Pest Control.

Pest Control, which did not respond to request for comment, has so far ignored the New York series, a sign Banksy didn't want the works sold, Madrigale said.

The overall street art market has steadily increased in value and Banksy's New York series has lent the genre legitimacy by bringing more widespread attention.

"For many people, this was really their first introduction to understanding this as fine art," Madrigale said.

However, not all artists have been included in the market's upswing.

5Pointz, an abandoned factory in New York's Queens borough that graffiti artists have used as a spray paint canvas for decades, was whitewashed this week by the building owner, who intends to demolish the building for a high-rise condominium.

Many of the graffiti artists, who tried to get the building landmark status, called the whitewashing "art murder", according to local media reports.

By midweek, someone spray painted over the paint, "You can try, but you can't whitewash this city."

Edited by Steve Wilson