"During those 10 seconds, your brain is actually doing something amazing," said Louis von Ahn, the Carnegie Mellon University computer scientist who invented this security system, called CAPTCHA, about eight years ago.

Computers are surprisingly bad at reading distorted images of words and converting them to text, he said. So he developed CAPTCHA to stop spammers from using computers to scrounge up hundreds of accounts, or scalpers from getting thousands of tickets.

But von Ahn said he was not satisfied that millions of people were going through his exercise. He was concerned about the 10 seconds it steals of consumers' time. If you look at the big picture, he said, "The whole of humanity is wasting millions of hours."

So he thought perhaps he could tap into this otherwise wasted human brainpower to help digitize old books, whose print is often faded. In such cases, computers make lots of reading mistakes - getting up to 30 percent of the words wrong.

So to solve two problems at once, he proposed using CAPTCHA to help with the book digitization, asking people to decipher words that had stumped the computers. He published his idea in last week's issue of the journal Science. Already dozens of firms have signed on, he said.

"Whenever anyone is buying tickets on Ticketmaster," he said, "They're not only stopping scalpers, they're also telling us what the words are saying in something that's been scanned and [is] being digitized."

- Faye Flam