Microsoft has an insect infestation to thank for its classic Windows XP desktop background—an image that has graced at least a billion computer screens since the system’s 2001 launch.

Napa Valley spent most of the 1990s trying desperately to curb the spread of phylloxera, a microscopic pest that was devastating its grapes. By the time the epidemic had run its course in 1999, some 50,000 acres of fields had been decimated.

Although the cost for growers was astronomical—half a billion dollars in total—the landscape of Northern California had never looked more idyllic. Endless rows of grapevines had been replaced by a lush carpet of grass, dotted here and there with wildflowers.

It was this vision of Sonoma County that flashed by Charles O’Rear’s car window as he drove down Highway 121 in 1998. Although he was a professional photographer, with work featured in National Geographic and the Los Angeles Times, O’Rear wasn’t on assignment that Friday afternoon. Instead, he was headed to visit his then-girlfriend (now-wife) near San Francisco.

But he still had one eye on the region’s rolling hills. It was January, and after the winter rains, “the grasses turn green and I know the chances of finding these beautiful hillsides are really good,” he recalled . “I’m going to be more prepared. I’m going to be more alert.”

And then, he saw it. “My God!” he thought. “The grass is perfect! It’s green! The sun is out, there’s some clouds.’”

So he stopped his car, pulled out his medium-format camera, and took a few photos using color Fujifilm. Those brilliant greens and pure blues were totally unedited when O’Rear uploaded them to Corbis, a stock photo and image licensing site founded by Bill Gates. A few years later, he got a call from Microsoft asking to use his shot of Sonoma County as the default background for its newest operating system.