As I was saying in a past–not so documented–article, this is how the Hidden Captcha concept works:
If yes, they’re okay — let’em comment, no annoying captcha required.
No? We’ve got a suspect. Read them their rights and serve them the ultimate “are you human?” test.
Here’s what you start with, the source code from this tutorial.
(Note: be sure to have the Arial font file called arial.ttf in the fonts folder–copy it from your System in there because their archive does not come with it).
<div id="captcha"> <img src="captcha.php" alt="" /><input type="text" name="code" /> Are you human? </div>