What is Captcha and Why is it Important?

 I am sure many of you have seen this(Captcha-check the image below) before and have wondered what is this and why is it always in websites?
What is a Captcha?
A CAPTCHA is a program that can generate and grade tests that humans can pass but current computer programs cannot. For example, humans can read distorted text as the one shown below, but current computer programs can't:


The term CAPTCHA (for Completely Automated Public Turing Test To Tell Computers and Humans Apart) was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford of Carnegie Mellon University. At the time, they developed the first CAPTCHA to be used by Yahoo.

Why is it important?

Captcha is important so as to stop computers from sending submissions. When used, computers won't be able to read it and that makes humans only. It also minimizes spamming.