CAPTCHA is a way for website owners to verify that a real user is filling out a form at a website. If a computer is filling out the form, then the CAPTCHA will fail, because a computer will be unable to read the image and output the text within the image into the form field.

Spammers try to automatically fill information into forms so that they can quickly and easily distribute their messages in mass on the web. This manual check makes it easier for spam control technology to stop this mass distribution of messages to unwanted places. The sheer economic burden of manually entering information into forms is deterrent enough to drastically reduce the amount of spam distributed.

Spam control technologies, such as CAPTCHA, have evolved over the years to keep up with the advances in technology of spammers. CAPTCHA images now include lines through the text that help to deter spammers from automatically reading the text within the images.

Advances in technology will continue to make it more difficult for spam to be effectively distributed. CAPTCHA is a great example of a technology that has created great difficulty for spammers who try to automatically disseminate their messages to online media consumption outlets, such as blogs, news sites, and forums.