Russel Brown, senior creative director of Adobe Systems, believes there may be a false sense of concern when it comes to changing images. "It's kind of like counterfeiting money," he says. "We could all put a dollar into a color copier and hit the button, but if we take a quick glance at that copy, we all know it's fake."

Brown acknowledges there are some extremely talented folks who can successfully alter a photo without leaving tracks. "But these people are few and far between. They will emerge, however, and if you pay them enough money, they'll be able to alter pictures so that, let's say, you're not in a crime scene or never had a mustache."

As with any technology, once the average consumer has access to it, it becomes a lot less coveted. "It's like the beginning of desktop publishing. When type became available to everyone, some pretty ugly things emerged. But as soon as the talented people got their hands on it, you started to see some really great stuff," Brown adds.

Digital cameras add another layer to the manipulation puzzle. An image taken with a digital camera creates a greater opportunity for mischief because there's no film involved. A picture is stored digitally in the camera's memory and then relocated to a computer's hard drive. It can then be saved, copied or printed.

But here's the real problem: A digital image can be copied continually with no degradation to the original because of the digital revolution's trademark--ones and zeroes. And there's no negative! The string of ones and zeroes which make up the image will always be the same--no matter how many times they're duplicated. The quality of an image made from a negative will lessen with each copy--bringing a lack of details and distinctness to these later prints. And the negative itself also is prone to degradation--which will affect the clarity of future photos as well.

Does this make anyone nervous? Yup. The FBI, for instance. Special Agent Douglas A. Goodin, an examiner in the FBI Laboratory's Special Photographic Unit, explains in a paper written in February 1996 entitled Image Security and Integrity: "The very nature of the computer that makes them so valuable for most of us, and so abhorrent to lawyers, is that it is by design an impermanent fixture. Data held in the memory is constantly being updated, with the old data (in most instances) being lost. Tapes and disks are continually updated to be current at closing time every day.

The ease with which images can be changed is the central issue in image integrity. The impermanent recording of an image by rearranging a bunch of magnetic particles and corresponding pixels seems to lack the security and integrity of good old film."

Goodin believes a greater problem for law enforcers may be when a digital camera is used at a crime scene. "The photographer may have been the only one there at the time. A particularly damning piece of evidence could be later undetectably inserted into the images through an image processing program. As digital photography becomes more widespread in law enforcement, I could see this becoming a problem for overzealous or dishonest officers," he warns.

What makes a good manipulation? There are many things to look at when trying to authenticate a photograph. In most cases, you'll probably be able to find some telltale signs that an image has been doctored.

One way is to blend two images together or play with the pixels of an image. In either case, there's a good chance you'll end up with jagged edges where things were cut or pasted. In general, photos don't have sharp edges. But if you paste one object onto a photo and zoom in close, you'll see the irregular pixels on the edge of that object.

The background in photos is another problem. Let's take Simpson's Brunos. If he was standing on asphalt and someone else wearing another pair of shoes was standing on concrete, the colors of the ground are going to differ. One will be on black while the other is on gray, so you'd have to move just the shoes without the background.

The obstacle in this process comes with the edge pixels of the shoes, which will turn out blurry when you paste them onto another photo. If you try to put gray against a black background, the pixels along the edge of the object will smudge, forming what might look like a halo. To fix this, you'd have to remove that halo, making the shoes look as if they were hovering in thin air--not too convincing.

Another issue is shadowing. Let's say you've got two images with lights coming from different areas in the picture. You'll probably be left with shadows pointing in two different directions. Even if they are pointing in the same direction, one shadow may be darker than the other. Again, that won't look very realistic if you try to change or move something. In order to fix this, there are tools such as "dodge" and "burn" which are used to make images darker or lighter, but you better have a pretty steady hand.

And don't forget film grain. When you take a picture, there's a certain amount of graininess--or coarseness--depending on when, where and how you take it. So if you're going to paste two images together, the grains of those pictures ain't gonna match. This creates a pretty big technical difference in the photo. To clean this up, there's something called a noise filter. Because noise varies the pixel, the noise filter helps create random patterns of lighter or darker pixels. This can create the illusion of a more average film grain. If you apply noise on top of an image that's been doctored, you may be able to mask some of the changes and imperfections by smoothing the picture out, making it more consistent.

There are many other problems to consider when doctoring an image--or looking for a doctored image. Odd shapes, inconsistencies of quality of light and changes in perspective are all dead giveaways. It's also why a person's testimony is now valued higher than a simple photograph. In fact, many lawyers believe in the dogma of "There are no perfect crimes--only imperfect investigations."

"I definitely believe it's possible to manipulate a photo without any signs," says Andrew Davidhazy, chairman of the imaging and photographic technology department at Rochester Institute of Technology and one of the experts asked to validate the authenticity of the Simpson photo. "The O.J. picture looked different than some other pictures on the roll, so what someone would have had to do, if those other pictures weren't found, is find out exactly where in the stadium the photographer was when he took the picture, check the color quality of the picture and check the negative to see if it was shorter or longer than the others."

Photographs have been questioned as evidence for many years--and there's no doubt that with the advent of digital technology, things are bound to get harder to authenticate. As Davidhazy points out, "It's just going to make it easier for people to he. Now we'll just have to count on the integrity of the photographer rather than the image itself."

PHOTO (COLOR): Michel Tcherevkoff in his computer

S (COLOR): Michel Tcherevkoff, our digital manipulator, used Barco Creator software to demonstrate how the Simpson photo--and his shoes--could have been doctored if someone were so inclined. Barco Creator was specifically designed for a Silicon Graphics Indigo 2 workstation, which is a high-speed, high-powered computer. The difference between this equipment and a PC or Mac using Adobe Photoshop, he says, is like the difference between a street car and a racing car--both get you to McDonald's but one gets you there a lot faster. In Tcherevkoff's doctoring, the foremost task was finding out what kind of film and lens were used on the original photo, so the original could be duplicated as close to perfect as possible. Also a big concern was O.J.'s posture. "He walks pigeon-toed," says Tcherevkoff. "So our model had to walk in two directions to get the shot just right."

The model now wears the rubber shoes and chick slippers.

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BY TOBEY GRUMET, Electronics Editor