Captcha Verify Images (PHP) นำไปใช้กับ formmail ได้บ้างครับ รบกวนด้วยนะครับ

<?php
//Check if form submit with capt variable
if(!isset($_POST['submit']) || !isset($_POST['capt'])) {
	//Form not submit return error
	exit("Error");
}

//session must be start to perform check
session_start();

//check input capt with session captcha
if($_SESSION['captcha']!=$_POST['capt'] || $_SESSION['captcha']=='BADCODE')
{ 
     //wrong captcha exit the program not continue.
	 exit("wrong code");
}