viz.

Scientific American has published a short guide listing five methods that researchers use to spot altered or retouched photographs.

For example, in the image above, some of the soldiers in the background have been “cloned” to make it appear that the crowd was more dense than it actually was.

While the guide details the mostly algorithmic methods used by Hany Farid and his fellow researchers, it also has some practical tips which can be used to identify altered photographs with the naked eye.

To infer the light-source direction, you must know the local orientation of the surface. At most places on an object in an image, it is difficult to determine the orientation. The one exception is along a surface contour, where the orientation is perpendicular to the contour (red arrows right). By measuring the brightness and orientation along several points on a contour, our algorithm estimates the light-source direction.

For the image above, the light-source direction for the police does not match that for the ducks (arrows). We would have to analyze other items to be sure it was the ducks that were added.

Related:
Digital forensics
Photo-retouching guru

The New Yorker recently published this profile of Pascal Dangin, the most sought-after photo retoucher in the world of high-fashion. Author Lauren Collins notes that retouchers are often forced to work in secret:

[R]etouchers tend to practice semi-clandestinely. “It is known that everybody does it, but they protest,” Dangin said recently. “The people who complain about retouching are the first to say, ‘Get this thing off my arm.’ ” I mentioned the Dove ad campaign that proudly featured lumpier-than-usual “real women” in their undergarments. It turned out that it was a Dangin job. “Do you know how much retouching was on that?” he asked. “But it was great to do, a challenge, to keep everyone’s skin and faces showing the mileage but not looking unattractive.”

Retouchers, subjected to endless epistemological debates—are they simple conduits for social expectations of beauty, or shapers of such?—often resort to a don’t-shoot-the-messenger defense of their craft, familiar to repo guys and bail bondsmen. When I asked Dangin if the steroidal advantage that retouching gives to celebrities was unfair to ordinary people, he admitted that he was complicit in perpetuating unrealistic images of the human body, but said, “I’m just giving the supply to the demand.” (Fashion advertisements are not public-service announcements.)

The article should be great fodder for studying the rhetoric of the body and the use of photography in our society.

The New York Times has posted an interview with Dartmouth’s Hany Farid, the creator of “digital forensics.” Here’s how Dr. Farid describes the field:

It’s a new field. It didn’t exist five years ago. We look at digital media—images, audio and video—and we try to ascertain whether or not they’ve been manipulated. We use mathematical and computational techniques to detect alterations in them.

In society today, we’re now seeing doctored images regularly. If tabloids can’t obtain a photo of Brad Pitt and Angelina Jolie walking together on a beach, they’ll make up a composite from two pictures. Star actually did that. And it’s happening in the courts, politics and scientific journals, too. As a result, we now live in an age when the once-held belief that photographs were the definitive record of events is gone.

Actually, photographic forgeries aren’t new. People have doctored images since the beginning of photography. But the techniques needed to do that during the Civil War, when Mathew Brady made composites, were extremely difficult and time consuming. In today’s world, anyone with a digital camera, a PC, Photoshop and an hour’s worth of time can make fairly compelling digital forgeries.

Dr. Farid makes some other interesting claims as well. Since 1990, the percentage of fraud cases involving photos has risen from 3 percent to 44.1 percent. While the majority of the interview focuses on digital manipulation in scientific research, clearly photographic forgery is becoming a significant problem in all areas of society.

Following up on Nate’s post about retouched photos, The Daily Show has revealed some contemporary presidential image-retouching: