Captchas have become a popular, though not impenetrable, method of keeping bots and automated scripts from abusing a website’s resources. The distorted strings of random letters and numbers over an obscuring background of gradients, speckles, and lines help ensure that the user of a web form or other server resource is a human, rather than another computer. — unless the person is blind or visually impaired. Captchas can’t be read or used by the screen reading software they use to surf the web.
In the Web Site Cookbook I wrote about a hosted Captcha service that makes it easy for website builders to implement captchas on their sites. Now the guys at captchas.net offer an audio alternative to their service, which is free for non-commercial use. You heard it here first.