Checkbox Captcha Wordpress Plugin is used by 4 websites. Among 4, 0 site is within top 10,000 and 0 site is within top 100,000 websites.
Wordpress Plugin Information of
|Plugin Meta Name||Plugin Meta Information|
|Plugin Description||Captcha made right!|
|Detail Plugin Description||
This is a tiny and simple plugin that helps fight spam on your site. All it does is add a checkbox in the comment form. When checked, the submit button is disabled. It's less intrusive than a text based captcha.
I strongly recommend using it with Akismet. Nothing replaces that, really. But Akismet can still create a bit of database usage, when confronted with a lot of spam. This plugin intends to help Akismet by giving it less to do. The main idea is not mine. I found a similar feature in Contact Form 7, so a bit of credit goes there.
During testing this plugin seemed to work better than text-based captchas. For reference without any captcha I had around 1000 spam comments per hour, with reCAPTCHA around 200, but with this method there are only about 2-3 spam comments per hour.
Wordpress Official Plugin Repository