CAPTCHA is one of the widely used techniques for preventing malicious programs from accessing the web resources automatically. In this paper compare spelling based CAPTCHA with other CAPTCHA. The proposed scheme, named Clickspell, introduces a new type of CAPTCHA system. It combines the features of text-based and image-based CAPTCHAs; Clickspell asks users to spell a randomly chosen word by clicking distorted letters for passing the test. Users can learn the definition(s) of the chosen word too. This is done by adding a cover image (advertisement) on the CAPTCHA image. So the users have to click the letters via a moving mask, making it harder for the malicious robots to attack.