The college says the collector, who wishes to remain anonymous, bought the photo in 1995 in Springfield. He brought it to the college's archive and special collections staff in 2007, and they've been researching it since.
Last month, it was publicly shown during the Emily Dickinson International Society conference in Cleveland, Ohio.
The daguerreotype, dated around 1859, appears to show Dickinson sitting next to a friend, Kate Scott Turner.
There's strong evidence it's Dickinson, including comparisons of high-resolution digital images of the newer photo with the known image, from 1847, said Mike Kelly, head of the archive and special collections department at Amherst College.
Kelly said perhaps the best evidence is an ophthalmological report that compared similarities in the eyes and facial features of the women in the photos. "I believe strongly that these are the same people," concluded the doctor who wrote the report. Researchers are also trying to get higher resolution pictures of the dress in the picture, to see if it matches fabric samples known to belong to Dickinson.
Researchers can't yet definitively say the photo is Dickinson, but "I think we can get beyond reasonable doubt," Kelly said
That could shift some perceptions about the Amherst native, Kelly said. For instance, a book in the 1950s was the first to propose Dickinson had a lesbian relationship with Turner, Kelly said.
"This is photographic evidence of their friendship, whatever the nature of that friendship was," he said.
The photo contradicts a misperception that Dickinson never left her house, when in fact she was quite social in her younger years, Kelly said. It also offers a strikingly different image from the existing photo of Dickinson as a frail, teen girl, which was taken before she began writing poetry. The newer image was taken when she was roughly 30.
"This is really when she's coming into the height of her powers," Kelly said. "To see her as this fully mature woman rather than this sickly little girl, I think it just shifts the way people think about what she's writing."
Amherst's collections department has a copy of the daguerreotype, which it says can be viewed on request.