For generations, our sense of what war is has been shaped by what photographers have sent back from the front – whether it be the squalid trenches of the first world war, the horror of concentration camps or the napalming of children in Vietnam. Some images, such as Robert Capa’s Death of a Loyalist Soldier, from the Spanish civil war, have become iconic.

The legendary photojournalists – Capa, Larry Burrows, Don McCullin and others – set out to document events and provoke reaction, not to create works of art to be hung on gallery and museum walls around the world. But increasingly, that’s just what’s happening to their pictures. Private collectors, too, are willing to pay huge sums for reportage images. In February, a print of W Eugene Smith’s photograph of a soldier holding a newborn baby, during the battle for the island of Saipan in 1944, sold at Christie’s New York for a greater-than-expected £4,269. In June 2007, three Larry Burrows prints of the Vietnam war fetched over £14,300 at another New York auction house.

And it’s not just grainy historical black-and-white images that are commanding such interest. Contemporary photographs from Iraq, Afghanistan and other conflict zones are also becoming collector’s items. The French photographer Luc Delahaye’s Baghdad IV, of a deserted road in the aftermath of a bomb blast, went for £22,100 at Sotheby’s in May. At the same auction, the British photographer Simon Norfolk sold an image of a bullet-scarred apartment building in Kabul for almost £6,000.

This year’s Brighton Photo Biennial takes the changes in both the production and consumption of war photography as its theme. Its curator, Julian Stallabrass, argues that, as fewer photojournalists are allowed on the front line, and censorship often dictates what can and cannot be shot, photographers have had to adapt to get their message across. Moreover, war is now as much about suicide bombs and terrorism as opposing armies. “The nature of war has changed dramatically, so the way we record it must change too.”

Hung in an exhibition, these images have immense visual impact. “You can only really appreciate them when you’re standing in front of them. If you put them out there for public viewing, get people to confront them and think and talk about them, it’s hugely valuable.” Whereas the typical 20th-century photojournalist used a 35mm Leica to snatch a shot while ducking bullets, many photographers today are turning to large-format cameras to create careful, considered images of war and its aftermath.

Simon Norfolk, who has been both acclaimed and criticised for his beautiful yet harrowing images of Afghanistan following 9/11, says it’s a case of finding new ways to communicate the horror of war to a compassion-fatigued public. “A sort of ennui has set in, which means that if you want to talk about war issues, you’ve got to find another way. I don’t care whether you think there’s nothing in my work – I want you to start debating our foreign policy, asking questions. Then I’m winning.”

The Brighton Photo Biennial: Memory of Fire: The wra of images and images of war runs from 3 October 3 to 16 November.

The Sublime Image of Destruction exhibition at the De La Warr Pavilion, Bexhill on Sea runs from 3 October to 1 January, 2009

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