"Photographs of torture victims are often so brutal and blatant that the viewer looks away. It's a reflex. Anonymous x-ray images can be viewed more objectively. The images make the viewer think about the issue of torture, but in a bearable way. That is my aim."

Professor Hermann Vogel has been collecting x-rays of torture injuries for almost 30 years. The project started organically; Vogel had just qualified as a professor of clinical radiology in Germany, and was travelling to developing countries to study the physiological effects of tropical diseases. "I was going through x-rays, and I began to notice that you have to pay special attention to Friday night. In the developing world, that is pay day and if you are paid, you drink, and then violence occurs."

Vogel realised the potential x-rays had for charting patterns of violence and uses of force worldwide. "At first I thought I should create an atlas about the radiography of war. I started to visit regions which had been or were at war, but as the project went on I knew it would be incomplete if I didn't deal with torture, too."

Obtaining x-rays proved tricky. "Victims of torture don't normally get treatment, or are kept in custody until the injuries are not apparent any more. The military regime in Chile dealt with evidence of torture by tying their dead victims to pieces of railway track and throwing them into the sea.

"I had to find other sources. I went to the rehabilitation centres of torture victims in Europe and Turkey, studied international x-ray archives and was sent material by colleagues who knew of my work. I was actually invited to Chad by a new regime which had just staged a coup. We were allowed to use two local hospitals to x-ray and find evidence of torture that had occurred under the previous regime."

For Vogel, the x-rays have a unique power. "X-rays reveal what the naked eye cannot see. A forensic investigation will reveal fractures, foreign objects and needles, but x-rays provide plausibility. Does the story match the pattern of injury? Does the age of the injury correlate with the time-span of when the torture occurred? Does the torture method correspond with the region, organisation, military or militia responsible?"

They also have a practical purpose, and Vogel is campaigning for the EU to accept the use of x-ray for non-medical reasons. "In some countries, x-rays can be used as evidence in court and a few of my x-rays have helped prove that torture has occurred. They are also increasingly being considered as part of the asylum process."

From the Guardian website, accessible here http://www.guardian.co.uk/world/2009/oct/31/x-rays-of-torture-victims. The image shown is of a knee-capping from Northern Ireland - the black dots are pellets.