Captcha is necessary part of any form. But if we see with end user point of view, a user feels bad when he/she has to give a right verification code and also have to face an error message if it is invalid code. “I don’t like Captcha and even i didn’t design any form with Captcha”.
If we give captcha verification using ajax, then it reduces user’s troubles.
We can check captcha on blur event or on submitting a form and alert the user about invalid code entered.
In Codeigniter ( i used it CI in some place ) it is easy to do that:
