Definition for CAPTCHA !

A CAPTCHA or Captcha is a type of challenge-response test used in computing to ensure that the response is not generated by a computer. ...en.wikipedia.org/wiki/CAPTCHA
Alternative capitalization of CAPTCHAen.wiktionary.org/wiki/captcha
A distorted image of letters and numbers used to prevent automated use of websites; Anything that a human must do to prove that they are not a ...en.wiktionary.org/wiki/CAPTCHA
CAPTCHA is an acronym for “Completely Automated Public Turing test to tell Computers and Human Apart”. ...lflegal.com/glossary/
Is used to decide whether a program or online service is being operated by a human or machine user.

One of the ideas I mentioned yesterday was making it more difficult for would-be spammers to post. Earlier today we pushed out a change that will prompt some users to solve a CAPTCHA if our spam classifier identifies the blog as spammy.We plan to quickly iterate on this approach a bit (as well as extend it to posts created via the API). So far, we have observed a slight decrease in the amount spam being created. There's clearly more to do.Update: Some users are having trouble solving the new CAPTCHAs and are seeing CAPTCHAs when they shouldn't be. We'll be pushing out a fix for that shortly.

It's important to know that if you are prompted to solve the CAPTCHA, it doesn't mean that there is anything wrong with your blog. Because of the number of variables our classifier uses, there's no easy way for us to pinpoint why your blog may have tripped the word verification (publicizing this information also serves to defeat the classifier).The number of false positives will affect only a small percentage of the overall Blogger community. However, I know that for those of you asked to answer the word verification that this is a true inconvenience and for that I apologize. We will be continually improving the classifier to reduce the number of false positives. We're also working on ways so that once a blog with word verification has been established as legitimate, the blogger will no longer need to solve the CAPTCHA.It's important that we find ways to put reasonable barriers in place to further prevent the automated creation of spam content. This is not just to prevent the contamination of search indexes with spammy search results, but to ensure the quality of Blogger's service for everyone.