The photographer whose image was used to try to discredit Democrat frontrunner John Kerry, says mainstream media can help to expose dirty tricks.
In the past week Mr Kerry has suffered two dirty tricks campaigns
"We act as an important filter in determining what is real and what is truthful," Ken Light told the BBC.
The fake photo combined two images to make it seem as if Mr Kerry shared a stage at an anti-Vietnam war rally in the 1970s with the actress, Jane Fonda.
The forgery was widely aired on the internet before it was exposed.
The revelation follows the rumour that Mr Kerry had had an affair with a young trainee reporter.
The forgery was posted on a rightwing website of Vietnam veterans who have long been critical of Mr Kerry.
Two British national newspapers - the Daily Mail and the Mail on Sunday - used the picture in editions last week and over the weekend.
Mr Light, from the Center for Photography at University of California's Berkeley, told the BBC's Today Programme he was "quite shocked", when he first saw the fake.
"It was my photograph with an image of Jane Fonda dropped in."
In the original one of Mr Kerry, he is sitting alone.
Mr Light said that the picture of Jane Fonda was taken a year after his own.
The photo, falsely credited to Associated Press, was circulated in the US to link Mr Kerry with a radical.
At the time of the photo, Jane Fonda was thought by many Americans to be a traitor for visiting North Vietnam during the war.
Mr Kerry, a decorated Vietnam hero, turned against the war when he came home.
"The mainstream media have risen up and revealed this hoax," said Mr Light.
"That is an important role we have in the media - to reveal these hoaxes."
"We just have to keep our eyes on photography and be careful what we see, and try to point out these things when we find them," he added.