Math Captcha is a 100% effective CAPTCHA for WordPress that integrates into login, registration, comments, Contact Form 7 and bbPress.
if requiered form field missed and filled in in second try, the plugin only says: time out.
no chance to reload the math only
used with Contact Form 7
I like a simple Captcha like this.
But in current Firefox, the math is wrong. If you try random numbers, it will finally accept it. But this is creating a barrier to commenting.
I brought it up in the support forum but no solution arose.
I also had a problem with it being messed up on the Comments form but managed to sort out the custom CSS for that.