Why am I asked to enter this code?

Why am I asked to enter this code? You must have asked this question yourself some time or the other. The code is to just confirm that you are human and not any automated program or spam. Yes, this code will keep spammers away from submitting your web form; it will protect your forum, blog, guest book, etc…
Technically this concept is called CAPTCHA (A CAPTCHA is a type of challenge-response test used in computing to ensure that the response is not generated by a computer). Ok this is all we can imagine by seeing that code image or questions like 2+2=? OR is fire Hot or Cold?
The reason behind why I took this topic is: We all will agree to fight against spam and we cooperate for that. But here people are taking this too serious and keeping multiple code images to enter before submitting or registering. Today one of my friends tried to register to Twitter.com and failed 7 times to satisfy that CAPTCHA code. He called me and asked hey Lax is this twitter working or down. We can’t blame him because after seeing that screenshot sent by him even you will feel the same.
Initially sites used to place single word to enter, but recently they advanced it to 2 words like as twitter asking. See the image above asked by Twitter. Hope this won’t advance more in future.
Source:TechZoomIn