Web applications often use CAPTCHAs to ensure that real human beings and not bots are using the system. These CAPTCHAs are mostly a combination of words that are distorted enough so that only human eyes can read and solve them.
Facebook is however taking a more social approach to CATCHA solving method.
Traditional CAPTCHAs are often hard to solve and therefore Facebook is experimenting with social authentication where you don’t have to recognize letters but images - they’ll show you a few pictures of your friends and ask you to name the person in those photos.Via Labnol
