It is the photograph that showed the true horror of Auschwitz extermination camp: murder on an industrial scale.
A train convoy can be seen bearing thousands of new inmates to the site; there are five crematoria, in which corpses from the gas chambers were burnt, and a huge plume of smoke spews from bodies burning in open pits.

Yet the picture, from 23 August 1944, was taken by accident, and Britain’s war leaders did not realise what it meant. Allied air reconnaissance planes flying at 15,000ft had been on a mission to photograph the Nazis’ IG Farben chemical factory, four miles away near Monowitz. The images were examined by Allied interpreters, who studied the plant in minute detail but failed to identify the rows of huts, gas chambers or crematoria. They then filed away the image without further analysis.

Yet in July 1944, even before the pictures were taken, Britain and America had already been urged to bomb the Auschwitz camp and the railway lines leading to it by the Jewish Agency, which had received reports of 400,000 Hungarian Jews being sent there.

David Cesarani, professor of Modern History at Royal Holloway College in London, explains: ‘By the summer of 1944, the British government knew that Auschwitz was a place of mass murder. Why, given this information, didn’t the Allies act sooner, and why specifically didn’t they bomb Auschwitz?’

The Observer | International | Could a photograph have saved thousands from the gas chamber?