Every web surfer, in the course of his or her browsing, has been forced to stop and perform this weird little task: look at a picture of some wavy, ghostly, distorted letters and type them into a box. Sometimes you flub it and have to retype the letters, but otherwise you don't think about it much. That string of letters has a name; it's called a CAPTCHA. And it's a test. By correctly transcribing it, you have proved to the computer that you are a human being.