Many a visitor to New York's Museum of Modern Art has probably thought, "I could do that," but a graffiti artist has gone one step further. A British graffiti artist who goes by the name "Banksy" smuggled in his own picture of a soup can and hung it on a wall, where it stayed for more than three days earlier this month before anybody noticed. The prank was part of a coordinated plan to infiltrate four of New York's top museums on a single day. The largest piece, which he smuggled into the Brooklyn Museum, was an oil painting, 61centimetres...