Norman Rockwell's Road Block is set to be the highlight of an American art sale at Sotheby's.
The extraordinarily complex work shows a host of characters attempting to cajole a dog out from under a truck.
It's expected to sell for around $4m-6m at Sotheby's New York on May 18.
The idea for the painting came from a story a friend told Rockwell about seeing a puppy sat in the middle of a road with a line of traffic backed up behind it.
Rockwell actually set up and photographed the scene in an alley in Los Angeles, a technique he used in most of his paintings.
He talked about the difficulties he had painting the work in a 1979 interview: "Why, oh, why do I paint such involved and complicated pictures?
"There are about twenty-five figures in this one, not counting the pigeons. My only excuse is that I wanted to paint this subject and I started to do the job with only ten people in it.
"Then, like Topsy, it 'just growed.' But here's the payoff.
"When I delivered it, the wonderful, kind and understanding art editor of The Post recognized the work I had put into it and gave me a substantial bonus over and above my regular price for a cover."
Rockwell's work is enormously popular, but has only recently started to set record sums at auction - with Saying Grace selling for $46m in 2013.
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