How to Create CAPTCHA Protection using PHP and AJAX CAPTCHA is a simple test to determine if a user is a computer or a human. It is used to prevent spam abuse on the websites. So if you use CAPTCHA on your web site forms, this can help in stopping some bots and making life harder for other bots in accessing or using your forms. Ajaxを使ったCAPTCHA認証をPHPで行うサンプル。 ページ遷移を行わないでCAPTCHA認証を行うことが出来ます。 仕組みとしては、