If You Use the Web, You May Have Already Been Enlisted as a Human Scanner

You're just about ready to buy a pair of tickets on Ticketmaster, but before you can take the next step, an annoying box with wavy letters and numbers shows up on your screen. You dutifully enter in what you see—and what a bot presumably can't—in the name of security.

But what you may not know is that you also have helped archivists decipher distorted characters in old books and newspapers so that they can be posted on the Web.

You might think that computer scientists would have figured out a way to get computers to decipher those characters. But they haven't, so instead they've figured out a way to harness all that effort you're making to protect your security. "When you're reading those squiggly characters, you are doing something that computers cannot," says Luis von Ahn, a computer scientist at Carnegie Mellon University (C.M.U.) in Pittsburgh.