Documentation
Captcha
The captcha helper provides a simple math captcha:
Methods
getMathQuestion()
Creates the question from random variables, which are also saved to the session.
correctAnswer(integer $answer)
Checks the given answer if it matches the addition of the saved session variables.
if (isset($_POST['submit'])) {
    if (Captcha::correctAnswer($_POST['answer'])) {
        // Do something...
    }
}