Now, we don't want to alarm you, but it's time you learned the truth. Magazines sometimes touch up photos of celebrities. I know. I know! It's shocking to think that Redbook might not be the absolute model of a journalistic commitment to the truth. But there it is. And here's a good way to deal with it.

As our sister site Jezebel has documented exhaustively, the magazine-world photoshop epidemic is impossible to escape. Legislation has been proposed to force magazines (ads included) to print disclaimers, like cigarette packs (in place of "lungs," think "self-esteem"), but another problem arises: how do you distinguish between minor retouching—erasing stray hairs, adjusting the contrast—and complete fantasy? The answer, as with so many things, is an algorithm:

The algorithm developed by Dr. Farid and Mr. Kee statistically measures how much the image of a person's face and body has been altered. Many of the before-and-after photos for their research were plucked from the Web sites of professional photo retouchers, promoting their skills.

The algorithm is meant to mimic human perceptions. To do that, hundreds of people were recruited online to compare sets of before-and-after images and to determine the 1-to-5 scale, from minimally altered to starkly changed. The human rankings were used to train the software.

Above, you can see the algorithm's work. It's not perfect—the "4" image looks more adjusted than the "5" to our eyes—but it's a start on a smart way to warn readers about the way the photos have been changed.