I implemented this as the last line in a suite of configs/addons to defeat bots that were able to pass captcha. I don't recommend any single addon as a solution for everything but this one really closed the gap once I was able to defeat bots that failed up to the captcha check.
Comments
Shumoo
thx for the help testing with Captcha registration in Vanilla 2.1 as well as providing the bug fixes for captcha.
I may not provide the completed solution you might desire, but I do try to provide honest suggestions to help you solve your issue.