"It was their most visceral, closest link to their loved ones," Zeller said. "For girlfriends or wives at home, the only thing they had was the ambrotype."
These images were taken by small-town photographers and traveling camp photographers, which combined topped 5,000 by the time war broke out in 1861, Zeller said. More than a million such images were produced during the war.
Officers had their photos taken as well and often passed them out to the men as a morale booster. New ways to reproduce photos gave birth to cards. The Library of Congress has produced an exhibit of soldier's portraits April 12 called "The Last Full Measure," based on a private collection.
The second kind of photo was the carte de visite. The carte de visite, or cdv, was also primarily a portrait photograph, except it was made with a glass, wet-plate negative, which meant unlimited copies could be created. Prints were made on albumen paper, according to the center. These portraits of generals, statesmen, actors and other celebrities were mass produced and given out like trading cards.
Some of the Civil War photographers, including Brady, have been criticized in recent years because it appears they moved corpses to create more graphic images. But Zeller said it wasn't a common occurrence. Given that each photographer need an entire wagon worth of equipment and chemicals, he said, these post-battle photographers faced their own set of challenges.
"Each time they moved, they had to secure bottles of chemicals and plate," Zeller said. "Each time they stopped, it had to be level." Photographers also battled flies that were attracted to photo chemicals, ether that made them woozy, and the stench of death.
"How they were able to look at the scenes of dead bodies and be calm enough to set up their equipment and try to portray reality, there is an unsung heroism there," said Alan Trachtenberg, retired professor of American history at Yale University. "It takes guts to do that."
Trachtenberg said military leaders on both sides also hired photographers to gain intelligence about enemy emplacements, roads, bridges and railroads.
Images of everyday life are also depicted for the first time in the Civil War, men playing cards, playing instruments or cleaning equipment. Black soldiers and slaves were also depicted for the first time, according to New York University professor Deborah Willis.
"The placing of the images was significant in identifying that black soldiers found their place in the war," Willis said. "They were working as soldiers and laborers. The fact is they also placed looked as if there are looking for hope."