In the previous chapter, we created a reddit news reader that was a bit complex from a coding point of view. To compensate for this, we will reduce our pace a bit in this chapter and develop various implementations of CAPTCHA.

CAPTCHA (short for Completely Automated Public Turing test to tell Computers and Humans Apart) is a form of test where web forms present questions to users that are supposed to be solved by humans only.

Imagine a simple registration form of a website. If you know all the fields present in the page, you can write a script to register as many times as you can.

Now, suppose a CAPTCHA challenge is placed in the registration form, where the user is shown 10 different colors and is asked to select a random color. A regular bot will not be able to do so and hence the registration will fail.