Captchas (Completely Automated Public Turing test to tell Computers and Humans Apart) are challenges designed to distinguish between humans and automated bots on the internet. These challenges typically involve tasks that are easy for humans to complete but difficult for automated programs. Over the years, several types of captchas have been developed to address various security concerns and usability issues. Here are some common types of captchas:
1. Image-based Captcha: In this type of captcha, users are presented with an image containing distorted characters or objects and are required to identify and enter the correct characters or objects into a text field. Image-based captchas may include various levels of distortion, noise, or overlapping to make it challenging for bots to interpret.
2. Text-based Captcha: Text-based captchas display alphanumeric characters in a distorted or scrambled form, making it difficult for automated bots to read. Users are asked to type the characters they see into a text box to prove their human identity.
3. Audio Captcha: Audio captchas are designed for users with visual impairments or those who may have difficulty solving image-based captchas. Users are required to listen to an audio recording of distorted speech and then enter the spoken characters into a text field.
4. Math-based Captcha: This type of captcha involves presenting users with a simple mathematical problem, such as addition, subtraction, or multiplication. Users must solve the equation and enter the correct answer to pass the captcha test.
5. Checkbox Captcha: The checkbox captcha is a more user-friendly option that only requires users to click a checkbox to confirm their human identity. However, sometimes additional verification steps are triggered if the system detects suspicious behavior.
6. ReCAPTCHA v2: Developed by Google, reCAPTCHA v2 presents users with a checkbox-style captcha with the message "I'm not a robot." In some cases, it may also ask users to select specific images that match a given criterion, like identifying all the images containing cars or street signs.
7. ReCAPTCHA v3: Unlike v2, reCAPTCHA v3 works in the background without any user interaction. It uses behavioral analysis to assess a user's browsing activity and assigns them a risk score. Websites can then use this score to take appropriate actions based on the perceived level of risk.
8. Honeypot Captcha: This type of captcha uses a hidden field in the form that is only visible to bots, not regular users. When bots fill in this field, the form submission is flagged as spam and rejected.
9. Social Media Captcha: Social media captchas are designed to encourage user engagement. For example, users may be asked to log in or register using their social media accounts, proving their authenticity.
10. 3D Captcha: These captchas use 3D images or require users to manipulate 3D objects to verify their human identity. They add an extra layer of complexity, making it harder for automated bots to solve.
These are just a few examples of the various types of captchas used to protect online platforms from automated bot attacks and maintain the security and integrity of their services. Captchas have evolved over time to strike a balance between usability for human users and effectiveness in deterring automated bots.