In the early 1960s, a jigsaw puzzle caused a sensation in America.
It was based on an abstract expressionist painting by the artist Jackson Pollock.
His explosive drip paintings had divided Americans into bemusement and outrage - he was a genius or a charlatan.
But the jigsaw was even more challenging than the original: it was proclaimed The World's Most Difficult Puzzle.
Alan Dein pieces together this bizarre story.