A CAPTCHA is a program that can generate and grade tests that humans can pass but current computer programs cannot. We need to add CAPTCHA validation on common form like contact us, enquiry Preventing Comment Spam in Blogs. Most bloggers are familiar with programs that submit bogus comments, usually for the purpose of raising search engine ranks of some website (e.g., “buy penny stocks here”). This is called comment spam. By using a CAPTCHA, only humans can enter comments on a blog. There is no need to make users sign up before they enter a comment, and no legitimate comments are ever lost!