THE PICTURE PROBLEM.

At the beginning of the first Gulf War, the United States Air Force dispatched two squadrons of F-15E Strike Eagle fighter jets to find and destroy the Scud missiles that Iraq was firing at Israel. The rockets were being launched, mostly at night, from the backs of modified flatbed tractor-trailers, moving stealthily around a four-hundred-square-mile "Scud box" in the western desert. The plan was for the fighter jets to patrol the box from sunset to sunrise. When a Scud was launched, it would light up the night sky. An F-15E pilot would fly toward the launch point, follow the roads that crisscrossed the desert, and then locate the target using a state-of-the-art, $4.6-million device called a lantirn navigation and targeting pod, capable of taking a high-resolution infrared photograph of a four-and-a-half-mile swath below the plane. How hard could it be to pick up a hulking tractor-trailer in the middle of an empty desert?

Almost immediately, reports of Scud kills began to come back from the field. The Desert Storm commanders were elated. "I remember going out to Nellis Air Force Base after the war," Barry Watts, a former Air Force colonel, says. "They did a big static display, and they had all the Air Force jets that flew in Desert Storm, and they had little placards in front of them, with a box score, explaining what this plane did and that plane did in the war. And, when you added up how many Scud launchers they claimed each got, the total was about a hundred." Air Force officials were not guessing at the number of Scud launchers hit; as far as they were concerned, they knew. They had a four-million-dollar camera, which took a nearly perfect picture, and there are few cultural reflexes more deeply ingrained than the idea that a picture has the weight of truth. "That photography not only does not, but cannot lie, is a matter of belief, an article of faith," Charles Rosen and Henri Zerner have written. "We tend to trust the camera more than our own eyes." Thus was victory declared in the Scud hunt--until hostilities ended and the Air Force appointed a team to determine the effectiveness of the air campaigns in Desert Storm. The actual number of definite Scud kills, the team said, was zero.

The problem was that the pilots were operating at night, when depth perception is impaired. lantirn could see in the dark, but the camera worked only when it was pointed in the right place, and the right place wasn't obvious. Meanwhile, the pilot had only about five minutes to find his quarry, because after launch the Iraqis would immediately hide in one of the many culverts underneath the highway between Baghdad and Jordan, and the screen the pilot was using to scan all that desert measured just six inches by six inches. "It was like driving down an interstate looking through a soda straw," Major General Mike DeCuir, who flew numerous Scud-hunt missions throughout the war, recalled. Nor was it clear what a Scud launcher looked like on that screen. "We had an intelligence photo of one on the ground. But you had to imagine what it would look like on a black-and-white screen from twenty thousand feet up and five or more miles away," DeCuir went on. "With the resolution we had at the time, you could tell something was a big truck and that it had wheels, but at that altitude it was hard to tell much more than that." The postwar analysis indicated that a number of the targets the pilots had hit were actually decoys, constructed by the Iraqis from old trucks and spare missile parts. Others were tanker trucks transporting oil on the highway to Jordan. A tanker truck, after all, is a tractor-trailer hauling a long, shiny cylindrical object, and, from twenty thousand feet up at four hundred miles an hour on a six-by-six-inch screen, a long, shiny cylindrical object can look a lot like a missile. "It's a problem we've always had," Watts, who served on the team that did the Gulf War analysis, said. "It's night out. You think you've got something on the sensor. You roll out your weapons. Bombs go off. It's really hard to tell what you did."

You can build a high-tech camera, capable of taking pictures in the middle of the night, in other words, but the system works only if the camera is pointed in the right place, and even then the pictures are not self-explanatory. They need to be interpreted, and the human task of interpretation is often a bigger obstacle than the technical task of picture-taking. This was the lesson of the Scud hunt: pictures promise to clarify but often confuse. The Zapruder film intensified rather than dispelled the controversy surrounding John F. Kennedy's assassination. The videotape of the beating of Rodney King led to widespread uproar about police brutality; it also served as the basis for a jury's decision to acquit the officers charged with the assault. Perhaps nowhere have these issues been so apparent, however, as in the arena of mammography. Radiologists developed state-of-the-art X-ray cameras and used them to scan women's breasts for tumors, reasoning that, if you can take a nearly perfect picture, you can find and destroy tumors before they go on to do serious damage. Yet there remains a great deal of confusion about the benefits of mammography. Is it possible that we place too much faith in pictures?

The head of breast imaging at Memorial Sloan-Kettering Cancer Center, in New York City, is a physician named David Dershaw, a youthful man in his fifties, who bears a striking resemblance to the actor Kevin Spacey. One morning not long ago, he sat down in his office at the back of the Sloan-Kettering Building and tried to explain how to read a mammogram.

Dershaw began by putting an X-ray on a light box behind his desk. "Cancer shows up as one of two patterns," he said. "You look for lumps and bumps, and you look for calcium. And, if you find it, you have to make a determination: is it acceptable, or is it a pattern that might be due to cancer?" ...