Michael Davidson was peering through his microscope at the tiny landscape of a silicon microchip when he saw it: A boy's face, nestled among the millions of tiny transistors. And he could swear the boy was smiling.

He closed his eyes, opened them again and pumped up the magnification.

No, he wasn't imagining things. It was Waldo -- the elusive hero of the "Where's Waldo?" children's book series -- his familiar smirk a fraction of the width of a human hair.

Although he didn't know it at the time, Davidson had stumbled onto the Lascaux Cave of the computer industry: A secret cache of microscopic doodles buried inside computer chips around the globe and known only to the small priesthood of bunny-suited engineers and technicians who created them.

"It really freaked me out because I'd never seen anything like it before," Davidson recalls. "I spent a lot of time trying to figure out if it was necessary to the circuit of the chip."

Davidson, a 48-year-old former biophysicist at Florida State University, now makes his living photographing invisible worlds. Using a $30,000 Nikon optical microscope with a built-in camera, he has captured the internal structures of substances that range from moon rocks to Ben & Jerry's Ice Cream to Fuzzy Navel cocktails.

His company, Molecular Expressions, earns as much as $500,000 a year selling these images to magazines as diverse as Discover and Pesticide Journal. His photos hang on the walls of the Smithsonian and the haberdashery racks of Bloomingdale's, where a New York neckwear maker uses his booze shots to adorn its Cocktail Collection ties.

"We can make up to $50,000 a month in royalties just from necktie sales," Davidson says.

But the mystery of microchip graffiti really caught Davidson's imagination, turning him into a digital archaeologist who spends weekends shucking chips from their black epoxy shells like a diver looking for pearls. He figures he explores 50 chips for each image he finds.

"I've spent an entire Saturday looking and not found a single one," he says.

Since uncovering Waldo three years ago, he's spotted dozens of other doodles: cartoon legends like Mickey Mouse, Donald Duck and Dilbert; film stars such as Groucho Marx; and a barnyard of mustangs, pit vipers and longhorn steers.

Who created these fantastic images and why? Davidson found out in the fall when he created an online gallery of microscopic Monets called "The Silicon Zoo" (http://micro.magnet.fsu.edu/creatures).

Soon after the Web site opened, some of the chip engineers who had created the images began sending him e-mail, explaining the history of their drawings, or pointing him to others yet undiscovered.

Among those who 'fessed up was Dan Zuras, a 45-year-old chip designer at Hewlett-Packard whose contribution to the Silicon Zoo is an image of the Road Runner. "I never thought I'd be alive when someone found it," he says.

Zuras says he spent nearly two weeks tattooing the Road Runner into a sliver of silicon that became a Hewlett-Packard math processor. The year was 1982, and this was his first solo design. At the time, the chip was the fastest of its kind -- hence his decision to stamp it with the Road Runner.

"I spent two years of my life on that chip!" says Zuras, "It's like a painter. When you're proud of your work, you sign it."

He squeezed the cartoon into an unused corner of his masterpiece, employing the same techniques he used to lay out the chip's transistors and street-like circuit patterns.

With a children's coloring book as his guide, Zuras traced the Road Runner into the design on his workstation. Later, the complete blueprint -- including the famous bird -- was used to create each thumbnail-sized microchip.

A complicated doodle may require designers to fool their own computers, because the software used to create chips is programmed to spot design flaws and often balks at odd angles.

But there's a good reason for trying. Unlike the music or film business, the computer industry has long prized anonymity. Few industry superstars receive acclaim for their work -- so creative minds resort to stealth.

The creators of the first Apple Macintosh had their names scrawled on the inside of every plastic hood. Atari programmers were famous for hiding secret messages called "Easter eggs" in their games. The messages, usually a list of the game's creators, were revealed only when players executed a specific sequence of moves. Easter eggs survive throughout the software business today.

Although no one knows exactly when micro-doodling started, it appears to be almost as old as the microchip itself. Davidson, for example, said he discovered a crude image of a sailboat on a Texas Instruments chip that "couldn't be newer than 1970 or '71."

Over the years, engineers have immortalized their nicknames, girlfriend's names, license plates, and favorite cartoon characters -- sometimes, all at once. Davidson has found as as many as 100 on a single chip.

Other discoveries are stranger still.

As a wedding present for a colleague who had just tied the knot, designer Kevin Kuhn etched profiles of the happy couple into a microprocessor -- a lasting if not very obvious tribute.

"It's not so much what you draw, it's the fact that you can do it. To be able to draw something so small it's just kind of amazing," says Kuhn, who works at Silicon Graphics in Mountain View, Calif.

Others have used the medium for good-spirited ribbing or revenge. After a friendly argument with a colleague, one engineer got back at his buddy by inscribing the message: "If you have any trouble with this chip, call " and filling in his buddy's name and home phone number. The phone never rang.

Sometimes these artistic urges can lead to trouble. Engineers tell tales of would-be Rembrants who short out a chip's circuity, causing it to malfunction.

As a result, some firms are less tolerant of impulse art than others. Davidson says he's never found a doodle on a chip made by the two American giants, Intel and Motorola, or on any Japanese chip. An Intel spokesman says its engineers may sign a chip only with their their initials, although one former Intel designer claims they can't be larger than the company logo.

"Very often management doesn't approve of this kind of thing," says Zuras. "It can grate on their nerves."

In this end, however, management may not have to worry. As microprocessors become more complex, so has the software used to design them. As a result, it's getting harder and harder to include cartoons.

But dedicated chip artists promise to carry on the tradition. "People will find a way to do it one way or the other," says Kuhn.