How Does CAPTCHA Work?

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every box that contains Alanis who are

we kidding we welcome all viewers

organic or robotic here at Tech quickie

but back on topic odds are you've

probably seen little tests like that

scattered around the internet when

you're trying to post a comment create

an account or buy something there called

CAPTCHAs which stands for completely

automated public Turing tests to tell

computers and humans apart proving once

again that the computer science

community continues to struggle with the

concept of acronyms anyway the irony of

using computing techniques to trick

other computers isn't really new leet

speak which goes all the way back to the

early 1980s originated as a method of

preventing content from being easily

searchable and to work around obstacles

like profanity filters a use that is

still common to this day but modern

CAPTCHA didn't come around until the

late 1990s when the then popular search

engine Alta Vista panelled was trying to

find a way to prevent BOTS or automated

computer programs from adding tons of

spam and malicious URLs to their linked

database they wanted to put some kind of

barrier in place and approach the

problem by thinking about something that

both humans and computers were good at

namely optical character recognition

which you can learn more about here then

introducing elements that made the task

much more difficult for computers while

keeping it fairly easy for humans and

since computers of the day could only

recognize clear easy to read text Alta

vistas engineers forced the user or the

bot as it were to read a puzzle with

distorted misaligned text with stray

marks in order to submit a URL to the


bass cool right this form of CAPTCHA

continues to be quite popular along with

audio CAPTCHA for the visually impaired

that in a similar vein typically

includes spoken letters that are

somewhat garbled to defeat automated

sound analysis guy2 w you'll see it

employed in situations ranging from

preventing BOTS from signing up for

social media accounts to cut down on

spam to verification on ticket buying

websites to ensure that BOTS working for

ticket scalpers can't snatch up all the

tickets to popular events you might even

see CAPTCHAs more frequently if you're

using a VPN service as many website

administrators are aware that VPNs are a

popular tool that scammers can use to

conceal their identities so a request

from a known VPN IP address is more

likely to trigger a CAPTCHA prompt but

there's a bit more to it than simply

presenting the scheming bot with a

confusing image capture scripts also

need to be written securely so that the

correct answer isn't available to the

bot through a backdoor for example some

CAPTCHA scripts especially many freely

available ones render the text on the

user's computer instead of on the server

and handle the answer in plain text

meaning that a bot can be written to

steal the answer without ever solving

the puzzle but even if proper security

is implemented bots are also getting a

lot more sophisticated than they used to

be and greater processing power has

enabled them to use machine learning to

get better at solving these kinds of

CAPTCHAs so everything from image

recognition puzzles to trivia questions

have been employed to stay one step

ahead of the spam bot arms race but

Linus what about those prompts that I've

been seeing these days that just say I'm

not a robot and then I just check a box

so I mean couldn't a robot do that how

does that work

well 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 mice in Wiggly

imperfect ways when they want to point

it something whereas this behavior is

usually absent with a bot no CAPTCHA

also looks at your IP address and cookie

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 user

increasing its popularity it's generally

regarded as reliable which is cool but

back to that face I made before it has

privacy advocates concerned about how

much information it's sending to Google

and how exactly is it being used oh that

Google but considering how many people

see an opportunity to make a quick buck

by deploying spam bots as the Internet's

influence continues to grow it isn't

likely we'll see the human verification

arms race cool down anytime soon I just

hope that it doesn't reach the point

where we have to submit like a DNA

sample and like a stool sample just to

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