You will probably be most familiar with the term CAPTCHA if you have ever entered a comment into a blog entry or website. It acts as a spam filter so that the webmaster won’t be bombarded with junk mail. It stands for completely automated public turing test to tell computers and humans apart.

CAPTCHA is essential if want to avoid been bombarded by unwanted e-mails. Users have to enter in text that is provided by the website in order to leave a comment or contact details. The text is usually letters or number and sometimes there is an audio sample of the text for visually impaired people.