As with photo age-progression "the science part only takes us so far," said Taylor, author of "Forensic Art and Illustration." "You have to connect those areas from dot to dot and the artistic hand must pass over it before it takes on a lifelike quality."

Reconstruction of Silvia Garcia. The sketch was recognized by people near the Austin lot where her bones were found in September 1995. She was positively identified through DNA from a licked envelope.

That artistic touch, along with educated guesswork, guides the use of modeling clay or two-dimensional drawings. Some assumptions, like the prominence of the jaw, are based on where muscles and ligaments were attached to the skull. Others are a bit less scientific.

If carefully manicured fingernails and fancy jewelry are found with female remains, for example, the woman may have been from a higher economic bracket and therefore might be given a fancier hairstyle and happier facial expression. Conversely, a male skeleton with neglected teeth found draped in three layers of shabby clothes may have been a homeless man.

"I wouldn't draw a happy expression on a person like that," said Taylor, who recently completed reconstruction sketches of a young woman dubbed "Valley Center Jane Doe" in San Diego.

As with age-progression, the ultimate goal of the reconstructions is to be anatomically correct but also to capture those hard-to-define qualities that may jog someone's memory.

"We think we recognize someone from their eyes or mouth but what really triggers the recognition is the overall essence of the face at a glance," said Taylor.

Karla Rodriguez, at 7 and age-progressed to 10. She was last seen in October 1999 walking to school in Las Vegas.

As time passes, Glenn Miller and his team of two forensic artists at the NCMEC try to keep up with some 3,000 kids in their database as they grow up.

Each week, they update about 10 age-progression images. Children under 18 get the virtual facelifts every two years. Then it becomes every five years as the process of aging slows.

Jacob Wetterling's photo has been aged at least three times, most recently in 1999 showing what he might look like at 21. The face is longer and slimmer but the dimple is still etched above the left side of his smiling mouth. Jacob's mom Patty has been persistent about getting the photo updated, sometimes ahead of schedule.

But just like the people who still call with tips about a missing 11-year-old, Patty Wetterling has had trouble identifying with the young man in the picture.

"It is very difficult," she said. "I also remember him as being 11 and my height."