| Zend_Captcha_Exception | Exception for Zend_Form component |
| Zend_Captcha_Adapter | Generic Captcha adapter interface |
| Zend_Captcha_Base | Base class for Captcha adapters |
| Zend_Captcha_Dumb | Example dumb word-based captcha |
| Zend_Captcha_Figlet | Captcha based on figlet text rendering service |
| Zend_Captcha_Image | Image-based captcha element |
| Zend_Captcha_ReCaptcha | ReCaptcha adapter |
| Zend_Captcha_Word | Word-based captcha adapter |