What is a CAPTCHA? What is it really used for? Types of CAPTCHA?

What is CAPTCHA? What is it really used for? Types of CAPTCHA?

CAPTCHA stands for "Completely Automated Public Turing test to tell Computers and Humans Apart". captcha is a technique to distinguish between humans and computers.

whenever you create an account in any website you solve a captcha code which determine  the user is a Human or Robots(computer and bots). 
computers or bots not capable to solve a captcha code but a human can solve it.

CAPTCHA is mainly used as a security check to ensure only human users can pass through. So, computers and bots are not capable of solving a captcha code.

Types of CAPTCHA?

CAPTCHA comes in several shapes, sizes and types.  These all work quite well against spam, but some are harder to solve and some are easy captcha.

most used captcha in  today time include:- 

1.  Text-Based CAPTCHA : In text-based captcha you can write same text as you can see in    image.

Text-Based Captcha

       2.Mathematical CAPTCHA : In Mathematical Captcha you can solve some simple                          equations .

2.  Mathematical Captcha

      3.Image-Based CAPTCHA : In image-based Captcha you can solve some image based                    questions.

3. Image-Based Captcha

       4. Re-CAPTCHA : Re-Captcha improve the captcha system. its tough on bots and easy for             humans .

Re-Captcha

       5. 3D CAPTCHA : In 3D based Captcha you can solve some text whose written in 3D.

3D Captcha