Going back to the start: what are captchas?

Captchas are deformed words that you are required to re-copy to validate and entry or for an action on the Internet. The principle behind captchas is finding an action that is easier for humans than for robots, so as to avoid the action you are doing to be done automatically (using robot-software). Especially to avoid millions of email accounts or Facebook accounts from being created automatically or to avoid a blog being flooded in comments to sell false Viagra. By re-copying the deformed text, you are proving that you are a human being (only from a biological point of view though!)