"The Derby Day" is an early version of one of the era’s most famous pictures — William Powell Frith’s teeming, picaresque image of the crowds at an 1850s horse race, from a rich family in their carriage to gamblers, acrobats and prostitutes.

The finished painting hangs in the Tate Britain gallery in London. The 15-by-35 inch oil-on-canvas sketch being sold by Christie’s is Frith’s first complete version of the scene.

Peter Brown, Christie’s director of Victorian pictures, said the rediscovery of the oil sketch was "immensely exciting."

It had been hanging in a modest New England beach house for decades before a friend of the owner suggested it might be worth something. Christie’s won’t be more specific about the location because the owner wants to remain anonymous.

Brown said the vendor, who is in his 60s, believes his parents bought the painting some time before World War II, when Victorian art was often dismissed as garish and sentimental.

"It’s a testament to the change in fortunes of Victorian pictures over the last century that these things could have been acquired very cheaply indeed in the ’30s, ’40s and ’50s," said Brown.

Since the 1970s, critical opinion has changed, and works by the best Victorian artists are coveted by collectors.

Frith, one of the era’s most successful painters, specialized in busy scenes of daily life, and his subjects ranged from beachgoers to railway stations to royal weddings.

"The Derby Day" was so popular when first exhibited in 1858 that a special rail was installed at the Royal Academy in London to hold back the crowds.

"It’s really a novel in paint and would have been read as such by the Victorian picture-going public," Brown said.

The painting goes on sale Dec. 15 in London, with an estimate of $477,000 to $800,000.