The moment Hungarian photographer André Friedmann and his German girlfriend Gerta Pohorylle decided to change their names was a hugely significant one in the history of photography. 

Friedmann was looking for a name that would make it easier to present himself as a French photographer to American magazine and newspaper editors, and as an American photographer to French editors, and which would mark him out from the other Jewish émigrés who had gravitated to Paris during the 1930s. So he borrowed from Hollywood actor Robert Taylor and director Frank Capra, and became Robert Capa.

The ploy helped - Capa went on to be described as "the greatest war photographer in the world" by the UK's Picture Post magazine. He took some of the most iconic war images of the 20th century, including the famous Death of a Loyalist Militiaman, in which he captured a Spanish soldier falling backwards at the very moment a bullet hits him in the chest.

Pohorylle meanwhile based her new name on the screen goddess Greta Garbo, becoming Gerda Taro. In her case, though, enduring fame as a photographer failed to follow. She became known for her romance with Capa, although many believe her own images stand comparison with her partner's. She organised Capa's career as a photographer and he taught her how to use a camera. Together they photographed the unfolding events of the Spanish Civil War in 1936, but she has received little of the acclaim accorded to Capa.

As Cynthia Young, curator of the Capa archive at the International Centre of Photography in New York, explains: "Many of Taro's prints were credited to Capa or they were jointly credited. Furthermore photographs of the Spanish Civil War were not republished afterwards, and by then Capa's name was better known than Taro's."

This is now set to change, with a display of Taro's newly discovered work at the Barbican in London, alongside a separate exhibition of Capa's work that looks at six of his iconic photo stories, including the Spanish Civil War and the D-Day landings.

It is claimed that Taro was the first woman to photograph at the frontline and the first photographer to die in action, aged 27, during the Spanish Civil War, in 1937.

Jillian Edelstein, a leading photojournalist who has covered South Africa, Kosovo and other conflict zones, is angry that she is so little known. "She was phenomenally out of her time for women and women photojournalists - and there are still very few women war photographers. Her photographs are groundbreaking for the time because she is there on the frontline," she says.

Many argue that Capa's and Taro's Jewish upbringing, and particularly their experiences as refugees from the Nazis, had an important influence on their outlook and work. Taro and Capa both left the native countries for Paris in 1933, and Capa fled again to America in 1939.

Natan Dvir, an Israeli photojournalist, believes that Capa was always very connected to his Jewish roots. "In the late 1940s he decided to go to Israel. His Jewish background allowed him to gain access and made him more sensitive to the various local people. For example, Capa made the first great images of the ultra-Orthodox community in Israel," he says.

Colin Jacobson, senior lecturer in photojournalism at University of Westminster and former picture editor of the Independent Magazine, agrees. "Capa's Jewish background made him into a humanist, concerned about social issues such as the Republican side of the Spanish Civil War and what was going on in the world."

This concern for humanity defined Capa's and Taro's work and re-shaped the images of war that remain familiar today. Young explains: "They photographed the people who were affected by war, the communities and towns that were destroyed and the refugees who were forced to move. It was a new angle of war photography and played into their profound understanding of what people were experiencing."

Their images confront the brutal human cost of war, from Taro's bomb-damaged victims stretched out in a morgue to Capa's American soldier killed by a German sniper, lying in a pool of his own blood, in Leipzig in 1945. But it is the intimacy of these images that make them so compelling, and as Edelstein points out: "There is a beauty in these tragic and tough situations which is unsettling."

The couple still exert an influence over today's war photographers. "Their work sets a precedent and people who go out to cover wars today look for similar things," says Edelstein.

As an example, Capa and Taro had an early understanding of getting close to the subject. As Capa claimed: "If your photos aren't good enough, you're not close enough."

This is a lesson that has certainly been taken to heart by Judah Passow, an award-winning photojournalist who has covered the Israeli-Palestinian conflict extensively. He says: "Capa's mantra still stands. Today the only way we photographers get pictures that really move people is by getting close to the people who are shaping the conflict - whether it is the combatants or the people working in the political background or the people caught in the middle. We want to pursue and expose the objective truth in covering a conflict. So we have to get as close as we possibly can."

Photographs by Gerda Taro and Robert Capa are displayed at Barbican Art Gallery, London EC2, until January 25 2009. Information at www.barbican.org.uk