Well, it's probably that most sites you get a captcha on, give one to everyone... this will only reduce that for real users.
On the flip side, there are other events to hook into... onfocus/onblur, keydown, etc, etc... which can all go into bot detection... if you fill out a form and didn't focus on anything, click on anything, or press any keys.. you're probably a bot... If you have JS disabled, you deserve what you get.
On the flip side, there are other events to hook into... onfocus/onblur, keydown, etc, etc... which can all go into bot detection... if you fill out a form and didn't focus on anything, click on anything, or press any keys.. you're probably a bot... If you have JS disabled, you deserve what you get.