One of the first examples to raise the issue, he said, was Time magazine's decision to darken the color of O.J. Simpson's skin on the cover of its June 1994 issue.
The magazine took the mug shot of Simpson when he was arrested and tweaked it before putting it on the cover. It was caught because Newsweek published an unadulterated version of the photo around the same time.
"O.J. was interesting because it was one that caught everyone's attention, he said. "It was the beginning of the public discussion."
In an editorial piece the week after the controversial issue was published, Time's managing editor wrote, "The harshness of the mug shot -- the merciless bright light, the stubble on Simpson's face, the cold specificity of the picture -- had been subtly smoothed and shaped into an icon of tragedy."
But to the National Press Photographers Association, those alterations changed the image from a document of reality to an editorial statement that deceived the public.
Another ethically-questionable image was featured on the cover of an August 1989 TV Guide.
The picture combined the head of Oprah Winfrey and the body of actress Ann-Margret, taken from a 1979 photograph.
The photograph was created without the permission of Winfrey or Ann-Margret and was detected when Ann-Margret's fashion designer recognized the dress, according to Hany Farid, a professor of computer science at Dartmouth College who studies imagery manipulation.
In another controversial magazine cover image, Martha Stewart's head was placed on top of the body of a slimmer model who had been photographed separately in a studio.
In 2005, Newsweek magazine placed the image on the cover of its magazine after Stewart was released from prison, ostensibly to highlight the many pounds she had shed.
The decision drew criticism from the industry with the National Press Photographers Association, calling it a "major ethical breach."
"NPPA finds it a total breach of ethics and completely misleading to the public," association president Bob Gould said in a statement at the time. "The magazine's claim that 'there was a mention on Page 3 that it was an illustration' is not a fair disclosure. The average reader isn't going to know that it isn't Martha Stewart's body in the photograph. The public often distrusts the media and this just gives them one more reason. This type of practice erodes the credibility of all journalism, not just one publication."
In 2006, Reuters was forced to fire a photographer, remove images from circulation and change policy after finding that a photo of an Israeli air raid on Beirut had been manipulated.
Bloggers were the first to notice that the clouds in an image taken by Adnan Hajj, a Lebanese photographer, had been darkened.
Soon after, Reuters issued an apology and said it withdrew from its database all of the images taken by Hajj. "There is no graver breach of Reuters standards for our photographers than the deliberate manipulation of an image," Tom Szlukovenyi, Reuters Global Picture Editor, said at the time. "Reuters has zero-tolerance for any doctoring of pictures and constantly reminds its photographers, both staff and freelance, of this strict and unalterable policy."