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What are the types of CAPTCHAS?

Fahad Farid

CAPTCHA stands for Completely Automated Public Turing Test to tell Computers and Humans Apart.

These tests are used to prevent automated programs, like web crawlers or bots, from accessing websites.

CAPTCHAs can tell humans and programs apart through a couple of distinct tests that users are required to take. Common CAPTCHA tests include:

  • having the user write text from an image or audio file into the answer field
  • selecting images that contain a particular object
  • clicking on a checkbox

The following list describes some of the types of CAPTCHAs:

  1. Math Problem: A user may be required to solve a math problem, such as 6x = 6, and write their answer in the box provided.

Pro: The problem is easy to solve.

Con: It may not be as secure as easier questions can be solved by computers using specific tools.

  1. Word Problem: A user may be required to solve a math problem such as, If John divides ten pencils among five people, how many pencils does each person get? The user will need to write the answer in the box provided.

Pro: Helps the visually impaired as it is not as difficult to solve as some other CAPTCHAS.

Con: This may not be as secure as easier questions can be broken.

  1. Time Based: The CAPTCHA calculates the time it took to enter the information. If this time is greater than a preset value, the user is assumed to be human.

Pro: It is easier to use and does not require user attention; therefore, it may seem less annoying.

Con: Users may not like to sign in with their accounts. This could result in a loss of web traffic.

  1. Confident CAPTCHA: A user may be asked to click on all the images containing a traffic light.

Pro: It is one of the most secure ones and has a high success rate.

Con: It is frustrating for the user and, if overused, the user may not revisit the webpage again.

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  1. Sweet CAPTCHA: This is similar to a confident CAPTCHA. A user may be asked to click on all the images that match the item shown. The user will have to pick the item and place it next to the ones that match, such as cow and grass.

Pro: It is one of the most secure and has a high success rate.

Con: It is frustrating for the user and, if it is over-used, a user may not revisit the webpage again.

  1. Social Media Login: A user may be asked to log in to social media. Bots do not have access to social media and, therefore, cannot log in.

Pro: Is a more secure CAPTCHA.

Con: Users may not like to sign in with their accounts. This may result in a loss of web traffic.

  1. Biometric CAPTCHAs: Mostly used for mobile devices. A user may be asked to place a finger on the fingerprint scanner of their mobile device.

Pro: It is not vulnerable to bots.

Con: If the finger is not placed properly, the CAPTCHA will fail.

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  1. No CAPTCHA reCAPTCHA: It asks the user to click on a box stating I am not a robot. This will capture mouse movements to determine if a user is human.

Pro: It is quick.

Con: If the test fails, the user will be presented with another CAPTCHA. Humans may become frustrated. Furthermore, Robots can be programmed to introduce randomization while clicking on the box.

  1. Invisible reCAPTCHA: It is similar to No CAPTCHA reCAPTCHA. This CAPTCHA is invisible and tracks user movement to determine if they are human.

Pro: It is quick, easy to use and does not frustrate the user.

Con: Robots can be programmed to introduce randomization while carrying out tasks.

  1. Honeypot: It adds invisible, hidden fields on the web page so that a bot will mistakenly type in the hidden fields when it types.

Pro: It is easy to implement and can be executed while in development.

Con: Visually impaired people using screen readers may see the box and fill it out by mistake.

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Fahad Farid
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