NEW YORK (NYT NEWS SERVICE ).- In Basel, Swiss authorities are prosecuting a local art expert who they say sold hundreds of fake prints that he passed off online as the work of Roy Lichtenstein, Andy Warhol, Paul Klee, Pablo Picasso and others over 10 years.

In New York, Adrienne R. Fields now spends much of her workweek scanning the internet for forged prints that pop up at website after website. She is head of the legal department for the Artists Rights Society, which protects the intellectual property rights of artists and their estates.

“It happens every day that Adrienne sends a ‘take down’ notice to a website,” said Ted Feder, president of the society.

The two cities, almost 4,000 miles apart, are both on the front lines of the fight against the sale of fake prints.

Since the dawn of the internet, the problem of phony art being sold has only grown, experts say, and the primary coin of the forgery realm has long been the fake print, which is relatively easy to create, often difficult to detect and typically priced low enough to attract undiscriminating novice buyers.

But now the problem seems to be escalating, according to law enforcement officials in the United States and Europe.

Timothy Carpenter, supervisory special agent of the Federal Bureau of Investigation’s art crime team, said that the proliferation of online art sales has deepened the problem. “Before, you had to find a way to get it to the market but e-commerce has changed the game,” he said.

The most prevalent fake prints are those falsely attributed to Lichtenstein and Warhol, experts said. But forgers have also brought to market multitudes of fake Picassos, Klees and Gerhard Richters, as well as phony works attributed to Marc Chagall, Joan Miró, Salvador Dalí and Henri Matisse.

Improvements in photomechanical reproduction techniques have made it easier for forgers to produce deceptive fake prints. “A real good reproduction can fool a lot of experts,” said John Szoke, a Manhattan dealer in Picasso and Edvard Munch prints. Detecting the forgeries is not simple, he said.

“It’s the color of the paper, the quality of the printing, the condition of the print, all of which you compare with the original,” he said. “And then you need years and years of experience.”

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