GumGum's Ophir Tanz Spins Gold from Ads on Images OnlineThis twentysomething innovator created a successful digital ad network for Web images. Learn how he did it. Part of our annual Young Millionaires report.

When he was 13, Ophir Tanz decided he'd never be able to work for anyone else. By 15, he had started his first company, an interactive branding agency called Fluidesign, which he sold before heading off to college. After graduating from Carnegie Mellon in 2004 with both bachelor's and master's degrees, a brief 10-month stint at the Bridgewater Associates hedge fund confirmed what he had long known: "It was a great salary, I learned a lot, but I just couldn't help myself," he says of his entrepreneurial leanings.

Now 29, Tanz runs Santa Monica, Calif.-basedGumGum, a digital network that places targeted advertisements over pictures online. "Basically, we pioneered a way for publishers to make money through ads on images," he says.