The Meaning of CAPTCHA: What It Is and How To Use It

You might have seen the word CAPTCHA on a web page during verification. This article will tell you what CAPTCHA means and how to use it.

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Have you ever wondered what CAPTCHA means when you see it as verification for a web page? This article will cover what CAPTCHA stands for, how CAPTCHAs are used, the types of CAPTCHAs, and other words that are related to verifications. 

Keep reading to learn all about CAPTCHAs! 

What Does CAPTCHA Mean?

According to CAPTCHA, this acronym stands for Completely Automated Public Turing Test to Tell Computers and Humans Apart. CAPTCHAs are used on websites for human verification and to prevent computer programs from hacking or spamming. The name is a reference to Alan Turing.

Visual-perception tasks like your typical CAPTCHA are often used during logins or when submitting online forms. After you enter your password in something like Gmail or another website login, a website might present you with a series of letters or a series of photos in a distorted fashion that you must decipher. 

Google owns a specific type of CAPTCHA called reCAPTCHA, in which users have to decipher distorted text or a series of letters. This type of CAPTCHA is very common. CAPTCHA technology is fairly recent, but its implementation has effectively prevented attacks and spambots.

What Is the Origin of CAPTCHA?

According to Phys, CAPTCHAs were first invented in 2000 at Carnegie Mellon University. The CAPTCHA system was invented by Luis von Ahn, Nicholas Hopper, Manuel Blum, and John Langford.

CAPTCHAs were created to prevent websites from being spammed by bots and programs. Many hackers and viruses can use websites millions of times a day, leading to massive website slowdowns and shutdowns. 

Over the years, programs have gotten better at solving CAPTCHAS, which means that programmers have had to make CAPTCHAS more difficult. Now, they are more difficult for both humans and computers to solve.

What Are Types of CAPTCHAs?

There are several types of CAPTCHA, including audio CAPTCHA, visual CAPTCHA, and written CAPTCHA. Below are several examples of CAPTCHAs:

First, a CAPTCHA might ask the user to solve simple math problems like basic addition and subtraction. Mathematical structures can be difficult for robots to solve.

One of the most common CAPTCHA forms is having to type in distorted text. Artificial intelligence may be good at reading normal text from an image, but when it is distorted, it is very difficult. 

There are also many image-based types of CAPTCHA. Some CAPTCHAs might require you to choose all of the images containing a certain object, like a bicycle or a bridge.

How Can CAPTCHA Be Used in a Sentence?

The term CAPTCHA can be used as an acronym to refer to the type of web page verification like how “Kleenex” is used for a tissue or “Band-Aid” is used for a bandage. You can learn how to use CAPTCHA in a sentence by studying the examples below.

The computer science students built a CAPTCHA to be used in the web forms for the university. These were used to prevent spammers from attacking the online polls, forums, registration forms, and other web services. 

They did not like how the CAPTCHA interfered with user experience but admitted that it was necessary to protect peoples’ credit card information. They could deal with a simple sequence of letters despite its drawbacks.

CAPTCHAs are designed so that the average person can solve them, but the average machine learning software or piece of artificial intelligence cannot. 

The computer scientists designed CAPTCHAs that were far too complex. The random words in the distorted image of letters were far too distorted, and no one could solve this type of challenge-response test.

What Are Synonyms of CAPTCHA?

CAPTCHA is a very specific term to refer to a type of web verification, but many other words can refer to a type of check or verification. 

CAPTCHA always has a tech and web connotation, but sometimes you might not want to use a word that has this type of connotation. Take a look at these synonyms of verification from Power Thesaurus to learn more.

  • acceptance
  • acknowledgment
  • affidavit
  • affirmation
  • analysis
  • approval
  • ascertainment
  • assay
  • assertion
  • assessment
  • attestation
  • audit
  • auditing
  • audits
  • authentication
  • authorization
  • avowal
  • certification
  • check
  • checking
  • checkout
  • checks
  • checkup
  • cheque
  • conclusive test
  • confirm
  • confirmation
  • confirmations
  • control
  • corroboration
  • crucial test
  • declaration
  • demonstration
  • determination
  • diagnosis
  • discovery
  • divination
  • documentation
  • endorsement
  • establishment
  • evidence
  • examination
  • experiment
  • identification
  • indication
  • inspect
  • inspection
  • investigation
  • permission
  • probe
  • proof
  • proving ground
  • ratification
  • reaffirmation
  • review
  • sanction
  • scrutiny
  • substantiation
  • support
  • test
  • testament
  • testimony
  • trial
  • validation
  • verification
  • verify
  • verifying
  • warrant
  • witness

What Are Antonyms of CAPTCHA?

Many words also refer to a denial or a lack of verification. If you fail a CAPTCHA, you might be faced with denial as a form of defense. Study these antonyms of denial Power Thesaurus to learn how to refer to the prevention of admission.

  • abandonment
  • abdication
  • abjuration
  • abnegation
  • abrogation
  • abstaining
  • ban
  • brush-off
  • confutation
  • contradiction
  • declination
  • defense
  • demurrer
  • denial
  • denied
  • denying
  • deprivation
  • disaffirmation
  • disallowance
  • disapproval
  • disavowal
  • disclaimer
  • disclaimers
  • dismissal
  • dispossession
  • disproof
  • dissent
  • embargo
  • exclusion
  • forswearing
  • interdiction
  • nay
  • negation
  • negative
  • no
  • nonacceptance
  • nullification
  • objection
  • opposition
  • prohibition
  • proscription
  • rebuff
  • rebuttal
  • recantation
  • refusal
  • refuse
  • refusing
  • refutation
  • reject
  • rejected
  • rejecting
  • rejection
  • relinquishment
  • renouncement
  • renunciation
  • repudiation
  • repulse
  • retraction
  • revocation
  • self-abnegation
  • self-denial
  • self-renunciation
  • turndown
  • veto
  • withdrawal
  • withholding


CAPTCHA stands for Completely Automated Public Turing Test To Tell Computers and Humans Apart. These verifications are often seen on web pages and web forms to prevent bots and spammers from compromising the websites. Numerous types of CAPTCHAs exist that are visual and auditory. 


  1. Captcha | 
  2. Verification synonyms – 634 Words and Phrases for Verification | Power Thesaurus 
  3. Denial synonyms – 904 Words and Phrases for Denial | Power Thesaurus 
  4. CAPTCHA: The story behind those squiggly computer letters | Phys