Sixty-one years ago, the photographic agency Magnum was founded over a boozy lunch in the restaurant of the Museum of Modern Art in New York by Robert Capa, Henri Cartier-Bresson and a group of other photojournalists seeking more editorial control. Driven by a humanitarian mission, Magnum encouraged a breed of brave photojournalists who ventured to where history was being made and documented what they saw.

The power of their pictures and those of other photojournalists grew until the 1960s when the Vietnam War became the most photographed war in history and one in which certain iconic pictures influenced American public opinion heavily.

Today all that has changed. Photojournalists are no longer the only ones taking photographs on the front line. Soldiers, insurgents, civilians and refugees all take photographs with their own cameras or mobile phones and can transmit them within minutes to their families or to the internet and news media. Brett Rogers, director of the Photographers’ Gallery in London, says: “With ‘embedded’ photographers and the emergence of soldier-generated imagery directly from the front line, the whole issue of how war is represented, by whom and how it is controlled politically has been thrown into question.”

Traditional photojournalists in the mould of Capa or Philip Jones Griffiths can no longer compete with instantaneous TV. So where do the photojournalists stand? “The need for images has not disappeared and it is now even more important for art to speak about political issues amid this proliferation of imagery,” says Kate Bush, director of the Barbican Gallery in London. “Photographers and artists still have a role as witnesses.”

The Barbican is devoting its entire gallery this autumn to war photography. Three exhibitions, curated by Bush, will be shown in parallel, the first on the work of Capa, the Hungarian-born photographer who made the famous 1936 image Death of a Loyalist Soldier during the Spanish Civil War. There have long been claims that the image was staged but the Barbican catalogue by Capa’s biographer, Richard Whelan, puts a strong case for its authenticity.

The second show covers the work of the little-known German photographer Gerda Taro, who spent her brief career photographing the Spanish Civil War alongside Capa, her lover and collaborator. She was one of the first female photographers on the front line and the first to be killed in action, in 1937, aged 26.

The third show covers the work of four contemporary artists Paul Chan, Omer Fast, Geert van Kesteren and An-My Le. Van Kesteren, for example, works in the conceptual art tradition but has been adapting documentary material from the internet, or from soldiers’ or victims’ testimonies, to make a powerful body of work that can shape opinions about the war. One of his works, Baghdad Calling, is a photo story based on the images made on mobile phones by Iraqi refugees, millions of whom have fled the conflict.

Van Kesteren’s work is also in this year’s war-themed Brighton Photo Biennial, curated by Julian Stalla-brass. There will be an exhibition of Agent Orange, Philip Jones Griffiths’s famous work from Vietnam, Harriet Logan’s images from Afghanistan, Frank Hurley’s work from the First World War and Thomas Hirsch-horn’s response to the War on Terror, a 60ft banner of the most atrocious and haunting pictures of humans torn apart by war that circulate on the internet but are never published in the mainstream media.

“People like Philip Jones Griffiths and Larry Burrows made amazing bodies of work in Vietnam,” says the photojournalist Tom Stoddart. “But after that the authorities clamped down heavily and photographers became embedded. Pictures come from elsewhere. Sometimes they come from within, such as the Abu Ghraib pictures. No journalist could have written a thousand words that would have persuaded Donald Rumsfeld to go on TV to apologise for that.”

When photojournalists are embedded they have to operate within parameters set, in Britain’s case, by the Ministry of Defence. No dead or wounded bodies can be shown; nor can mortuaries, coffins, even damaged buildings.

Since we do still need images for our news, photojournalists must find a new language. We do not need more clichés – palatable pictures of soldiers silhouetted against a dusky skyline. What we want is work that challenges our preconceptions and provokes the imagination to think through horrors happening far away. We need to see the Baghdad flower seller who sets up her stall a couple of days after the suicide bomber destroyed the railway station.

We need to see what devastation one piece of shrapnel can do to a family. We need to be made to think about how survivors have to get on with their lives in these places, because the power of war photography to shape politics, opinion and lives remains real.

This is War! Robert Capa at Work; Gerda Taro, a Retrospective; On the Subject of War: Artistic Responses to Iraq and Afghanistan, Barbican Art Gallery, London EC2 (www.barbican.org.uk 020-7638 4141), Oct 17-Jan 25. Brighton Photo Biennial 2008, Memory of Fire: The War of Images and Images of War, University of Brighton, Grand Parade, Brighton (bpb.org.uk 01273 643052), until Nov 16 2008

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