How does CAPTCHA work?

You’ve probably seen little tests scattered around the internet when you’re trying to post a comment, creating an account or buy something. These tests are called CAPTCHA which stands for “Completely Automated Public Turing test to tell Computers and Humans Apart” is a type of challenge-response test used in computing to determine whether or not the user is human. It’s mainly used as a security check to ensure only human users can pass through. Generally, computers or bots are not capable of solving a captcha.

It’s generated by distorting an image with misaligned text/numbers, in such a way that any OCR technology fails, and only a human eye can read and make sense. Till date, there are no good automated captcha solving algorithm.

However, one can notice that captcha are getting harder as time progresses. This is because, usage of latest advanced pattern recognition and machine learning algorithms are capable of solving a simpler captcha, so the latter should be in a position to defeat the former.

Nowadays you may notice prompts that just say “I’m not a robot”, how does that work?

This is a pretty cool mechanism from Google called “no CAPTCHA”, it actually tracks your mouse movements right before you check the box, humans tend to move their mouse in wiggly imperfect ways when they want to point at something whereas this

behavior usually absent with a bot.

“no CAPTCHA” also looks at your IP address and Cookies activity to see if it’s probably consistent with a human instead of a bot and this automation has made it much faster and less frustrating for the users. We just hope that it doesn’t reach the point where we have to submit a DNA sample just to make a comment on a website.