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:

1. they force the burden of work back on your commenter and pushing extra work on your readership displays a lack of respect
2. they show you are too lazy to properly secure your blog against comment spam (using blacklists, .htaccess, number of links, etc.) and most importantly,
3. they discriminate against partially-sighted readers

There are many good anti-comment spam tools and procedures available, don’t use captchas.