The different types of CAPTCHA available are as follows:
- Reading-based CAPTCHA: These are visual preceptors. They include text recognizers and image detectors. These are difficult to crack, but the downside is that they cannot be accessed by visually impaired persons.
- Speech recognition-based CAPTCHA: These are audio CAPTCHAs. Like visual CAPTCHAs, they are complicated audio representations of a jumble of words with or without context.
- Graphical CAPTCHA: These are sophisticated forms of visual CAPTCHA. Graphical CAPTCHA is also almost impossible to crack by software.
- Smart CAPTCHA: When CAPTCHAs are fused with JavaScript, their complexity increases exponentially. Malicious bots find it difficult to parse JavaScript.
- MAPTCHA: These are mathematical CAPTCHAs. However, they require cognitive intelligence to crack.
- Logic/trivia: CAPTCHA often asks logical questions and puzzles. However, little is known about the amount of resistance that CAPTCHA provides.
The following screenshot shows the different CAPTCHAs:

There are also other types of CAPTCHAs available, as shown here:
