CAPTCHA How Does It Work?

bluelass

I have seen this on many sites and used it myself but how does it work and what is its purpose?.

esuhl

It's purpose it to determine whether you are a human visitor trying to access to site, or whether the access attempt comes from an automated script.

dipsomaniac

i think i have read somewhere that it also helps to confirm text in scanned documents and books

Doshwaster

"Completely Automated Public Turing test to tell Computers and Humans Apart"

Double_V

There is also reCAPTCHA now.

kwikbreaks

Some are pretty much impossible for humans too. A necessary evil unfortunately.

paddyrg

The idea is to give a task that's easy for a human and hard for a machine. If you've ever tried to OCR a scanned document, you'll know that reading printed text is error prone for machines, especially with swirly lines and non-dictionary words.

The CAPTCHA systems that present two words are usually used to solve poorly OCR'd scanned historic works - one word verifies you're human, the other creates a consensus about what type was scanned.

More popular now are 'click on all the cats' type - an array of 8 or 9 photos where 3 may be cats, the rest dogs, lions, ferrets, etc.

These have the byproduct of assisting machine learning - if a big compute engine manages the images shown appropriately, it can learn to spot cats by itself!

ARandomMiser

Even the 'i am not a robot' checkbox uses mouse movement to determine if you are a bot

cookie365

The ones with 2 words are quite clever.

There are various projects going on to scan and OCR important printed texts, and there are always some bits of text that the computer can't read with certainty.

One of the images is a known word, the other is the text that's unknown. You only have to get the known word correct for the purposes of the captcha, what you type for the second word is effectively a vote for your interpretation of it. Use the image enough times and you'll get a consensus on what the word is.

Oblivion

Here at Oblivion Enterprises we are working on a derivative of CAPTCHA which ensures you input your bank details correctly. :cool:

maman

For the past couple of days I've been getting a CAPTCHA 'Are you a robot?' message when posting on mse. It's never happened before. Anyone know why and what I can do about it?