My knowledge of php is not good and I need help.
I have this php form but I don't know how to add a CAPTCHA mechanism.
How do I achieve this?
I really like Securimage is seems to work really well and does not require a third-party external service or javascript (unless you enable the new image feature). Also it can be configured to provide audio captcha for accessibility.
Check this detailed guide about captcha implementation in PHP: http://www.the-art-of-web.com/php/captcha/
来源：https://stackoverflow.com/questions/2179375/how-do-i-add-a-captcha-to-my-php-form