In the 150 years since a Swiss businessman, Henry Dunant, horrified by the carnage of battle, had the idea that was to become the Red Cross, photography has changed out of all recognition.

Yet the reality of war, and the work of the International Committee of the Red Cross (ICRC), remain the same: bringing humanity and kindness to the lost, injured, dispossessed and traumatised.

Photographer Nick Danziger has been on assignment for the ICRC in war zones from Chechnya to Afghanistan and the Balkans.

“They’re all harrowing but rewarding,” he says. “Working for the Red Cross is a privilege but also a burden: the stories you’re telling are so important that the pictures can rarely match up to what the people in the images are going through.

I am in awe of the staff who work on the ground, the local workers and field officers who offer assistance when others are fleeing. Photography is not the priority of the Red Cross, but everyone is aware of how much an image will say about their work.”

The ICRC has an archive of more than 100,000 images, dating back to 1860 and now the subject of a book and exhibition, Humanity in War.

“Photography emerged at about the same time as the Red Cross movement 150 years ago,” says Sir Nick Young of the British Red Cross. “One task of a photographer is to reveal the unjust and the unacceptable, so photography is an important complement to the work of humanitarian organisations.”

The sadness, suggests Danziger, is that so many of the pictures are recent, and close to home – “I think,” he adds, “the humanity is in those extraordinary people who stay behind to help.”

As fellow photographer James Nachtwey puts it, “Often the worst circumstances can bring out the best in people… When I look at the pictures in this book, I can’t help but think how much worse things would have been if the ICRC hadn’t been there.”

The free exhibition Humanity in War: Frontline Photography since 1860 is at the Oxo Tower, London SE1, from July 8-19

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