What is Image Verification ("Captcha")?
Image Verification is a security test that screens non-human users (i.e., bots). Display of the security pass code as a randomized, distorted image is intended to frustrate all but the most sophisticated computer programs, few of which are capable of extracting word/letter/number combinations from an image. This extra security step should ensure only human users access to the form. Captchas are now in widespread use on the World Wide Web, effectively combating bot-generated spam.