Completely Automated Public Turing test to tell Computers and Humans Apart, (CAPTCHA) determines whether the computer user is real or a spam robot. CAPTCHAs were invented to block spammy software from posting comments on pages or purchasing excess items at once. The most common form of CAPTCHA is an image with several distorted letters. It is also common to choose from a variety of images where you need to select a common theme.

CAPTCHA has a variety of applications for keeping websites and users secure. These include but are not limited to:

- Protecting email addresses from scammers

- Protect website registrations

- Protects online polling

- Protects against email worms/junk mail

- Prevents dictionary attacks

- Prevents comment spamming on blogs

More Info: www.google.com