What is a CAPTCHA?

A CAPTCHA is an acronym 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 is a test to tell computers and humans Apart.

In order to ensure that only humans can access certain areas of a website or online service, webmasters may use CAPTCHA tests. A CAPTCHA test requires users to complete a task that is easy for humans to solve but difficult for computers. This might involve identifying letters and numbers in a distorted image, answering a simple question, or completing a basic puzzle.

CAPTCHA tests are used for a variety of security purposes, including preventing automated software from signing up for online services, or submitting spam comments on websites. They can also be used to slow down brute force attacks on login pages.

While CAPTCHA tests are effective at deterring bots and other automated software, they can also be annoying for human users. In some cases, CAPTCHA tests can be difficult to read, or may require users to complete multiple tests in order to gain access to a service. As a result, some webmasters are looking for alternative ways to verify that users are human.

Applications of CAPTCHAs

CAPTCHAs have several applications for practical security, including (but not limited to):

  • Preventing Comment Spam in Blogs. Bloggers are frequently familiar with programs that submit fraudulent comments, usually for the goal of improving a website’s search engine rankings (e.g., “buy penny stocks here”). This is referred to as comment spam. Only humans can post comments on a blog using a CAPTCHA. There is no need to make users sign up before they enter a comment, and no legitimate comments are ever lost!
  • Protecting Website Registration. Several companies (Yahoo!, Microsoft, etc.) offer free email services. A few years ago, many of these services were being attacked by “bots” that would sign up for thousands of email accounts every minute. To solve this problem, the companies began using CAPTCHAs to ensure that only humans could obtain free accounts. Generally, free services should be protected with a CAPTCHA to prevent abuse by automated scripts.
  • Protecting Email Addresses From Scrapers. Web scrapers search the internet for email addresses that are not hidden. CAPTCHAs help to protect your email address from being seen by these scrapers. The way it works is by making people solve a CAPTCHA before they can see your email address. A simple yet effective approach to hide an email address using CAPTCHAs is available at reCAPTCHA MailHide.
  • Online Polls. CAPTCHAs can be used to ensure only humans take part in online polls. This is particularly useful for polls on sensitive topics, or where there might be a temptation to “stuff the ballot box” with fake votes.
  • Preventing Dictionary Attacks. CAPTCHAs can also be used to prevent dictionary attacks on passwords. The idea is simple: a computer can’t try different passwords if it has to solve a CAPTCHA after a certain number of unsuccessful logins. This is better than the traditional way of locking an account after a certain number of unsuccessful login attempts. This way, an attacker can’t lock your accounts at will.
  • Search Engine Bots. Sometimes you may want to keep web pages hidden from other people. You can do this by using a tag that tells search engine bots not to look at the page. However, this doesn’t mean that the bots will definitely not look at the page. Because search engine bots are often associated with large companies, they will not violate web pages that do not want them to enter. However, because CAPTCHAs are required to ensure that bots do not enter a website completely,
  • Worms and Spam. CAPTCHAs are another approach to fight email worms and spam. “I will only accept an email if I can verify that the other computer is operated by a person.” This concept has already been marketed by a few firms.

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