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The pictures had been digitally altered to disguise the man's face with a swirly pattern, but computer specialists at Germany's federal police agency, the BKA, worked with Interpol's human trafficking team to produce identifiable images.

The global police body said it was making the unique public appeal because, despite extensive efforts through its network of 186 member states, the man remained unknown.

"For years, images of this man sexually abusing children have been circulating on the Internet," Interpol Secretary General Ronald Noble said.

"We have tried all other means to identify and to bring him to justice, but we are now convinced that without the public's help this sexual predator could continue to rape and sexually abuse young children whose ages appear to range from six to early teens."

Photographs of the man are available on Interpol's Web site, www.interpol.int and anyone with information on him is urged to contact their local police or Interpol's human trafficking unit.

Anders Persson, a Swedish police officer seconded to the unit, told Reuters the dark-haired man in the photos was thought to be a European aged around 35-40.

He said a child abuser seeking contact with like-minded individuals on the Internet would sometimes post pictures of himself in the act of abuse as a kind of "ID card" to prove he is a genuine hard-core pedophile.

The inquiry began when the first pictures of the man were found by German police in 2004. A link to a Vietnamese hotel emerged from advertising material seen on a bedside table in some of the pictures, Persson said. But checks against passport photos of people on the hotel's guest list drew a blank.

Other photos were taken at outdoor locations in Cambodia that were recognized by police there.

Interpol runs a huge database of images of child sex abuse and uses sophisticated software to find connections between them, even analyzing tiny details like wallpaper and fabric patterns in apparently anonymous indoor settings.

Now containing more than 520,000 images submitted by 36 member states, the database has helped police identify and rescue nearly 600 victims from 31 countries to date.