A captcha is an acronym for “completely automated public Turing test to tell computers and humans apart – in other words a type of challenge-response test used to determine whether or not a computer user is human (or another computer).
From the Wikipedia entry on Captcha’s:
A common type of captcha requires that the user type the letters of a distorted and/or obscured sequence of letters or digits that appears on the screen. Because the test is administered by a computer, in contrast to the standard Turing test that is administered by a human, a captcha is sometimes described as a reverse Turing test
Recently, I have seen several bloggers install captcha’s as a way to try to stop comment spam on their site – guys, captcha’s are lame.
Why are captcha’s lame? Captcha’s are lame because:
- they force the burden of work back on your commenter and pushing extra work on your readership displays a lack of respect
- they show you are too lazy to properly secure your blog against comment spam (using blacklists, .htaccess, number of links, etc.) and most importantly,
- they discriminate against partially-sighted readers