The card, an 1865 photo of the Brooklyn Atlantics, is so rare it is one of only two known in existence. The other? It's in the Library of Congress.
The card was discovered by an antiques picker in Baileyville, a town of about 1,700 people in rural Washington County, the Portland Press Herald said.
"Any auctioneer in the country would want this card,” said Floyd Hartford, of Saco River Auctions in Biddeford, Maine, who will put up the piece of baseball history.
Saco River Auctions set a record in August for the sale of a 1888 Michael "King" Kelly card for $72,100, but auction house manager Troy Thibodeau said the Atlantics card should eclipse even that impressive sum.
"If the other one was a home run, this is a grand slam," Thibodeau said. "It will make huge waves in the industry."
Baseball trade cards began to appear in the late 1860s featuring individual players as both baseball and photography became more popular. The earliest trade cards are believed to have been distributed by Peck and Snyder, a sporting goods store in New York, as an advertising vehicle.
According to the Press Herald, the picker who discovered the card was looking for furniture at a yard sale, but instead found the photo album containing the baseball card in a woodshed.
A Boston-based photo conservator Paul Messier authenticated the card Monday in a process that took $700 and nearly 6 hours.
The card is a "carte de viste" a small photograph usually made of albumen print, mounted on thicker paper. It shows the ten players of the Atlantics, a team that was dominant in early baseball and won championships in 1861, 1864 and 1865.
The Brooklyn Atlantics card will go up for sale on Feb. 6 at 5 p.m. in Biddeford, Maine.