A new exhibition documents American photography's first 70 years, exploring the US during a period of immense social, geographical and industrial change.

Modern culture is indebted to photography. "We can't be literate in today's world if we don't know how to make and share and interpret images", Jeff Rosenheim, photography curator at New York's Metropolitan Museum of Art, tells the BBC. "And when did camera culture become so much a part of all of our lives? It actually started in the 1840s and 50s."

Though originating in Europe, "the speed with which this medium took hold in the US is one of the great surprises," says Rosenheim, who, thanks to the incredible range of early American images in the William L Schaeffer Collection, a recent gift to the museum, saw an opportunity "to tell an expanded story about the birth of this medium".

The New Art: American Photography, 1839-1910, which opened on 11 April, documents American photography's first 70 years through 225 photographs, reversing the usual top-down approach by focusing on unknown makers that tell nuanced stories about the US during a period of immense social, geographical and industrial change.

"I quickly realised that there was fantastic picture-making, really important stories, outside of the big cities, all across the country," says Rosenheim. One such story is embodied in an anonymous 1950s daguerreotype (an image created on silver-coated copper plate) of a young man holding a chicken − a man for whom a painted portrait was probably unaffordable. But, thanks to this new art, he had made his way to a studio, along with his feathered companion, to receive his likeness.

Holding the pose – sometimes for minutes rather than seconds − was essential to a good image, and the bird's minimal blurring suggests it was at ease in the boy's arms. Though photography was in its infancy, the sharpness of the image, from the boy's freckles to the rooster's scaly feet, is remarkable. The young farmer's photograph captures the spirit of the American pioneers and is filled, says Rosenheim, "with pride and optimism for his own future".

It would be another decade before the US would abolish slavery, and a century before the Civil Rights Act prohibited racial segregation. As a result, the theme of agency is implicit in many of these early images. An 1850s daguerreotype of a woman wearing a tignon (cloth turban) is a reminder of the Tignon Law in colonial Louisiana that required free black women to cover their hair. In response, some women reclaimed the tignon as an object of beauty and pride. This elegant portrait, with its extraordinary detail − from the delicately carved earrings to the weave in the translucent shawl − provides an opportunity for positive self-representation against a background of racial discrimination and negative stereotyping.

For the 19th-Century US, the making of these images was a spectacle in itself. In a rare photograph printed on salted paper around 1855, we see this wizardry at work. "There's this sort of magic about photography, that you have to go into the box itself, in a certain sense, and cover your head to make a picture," says Rosenheim. But for all the photographer's mastery, they are never entirely in control. Edward's Steichen's famous 1903 portrait of JP Morgan is an example; it inadvertently conveys his impatience with posing, and an innocent object – the chair handle – appears like a dagger in his hand.

"The world coalesces and comes together in ways that the photographer intended and did........

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