There are several types of captcha tests available for use in email marketing:
Text-based Captchas: Users are asked to enter characters displayed in a distorted image. Image-based Captchas: Users must select images matching a given description, such as "Select all squares with traffic lights." Audio Captchas: Users listen to an audio clip and type the spoken words, useful for visually impaired users. Invisible Captchas: These work silently in the background, analyzing user behavior to detect bots.