I am using the SI Captcha plugin which works on all pages and posts but my registration page.
It is there but the image does not show up so you can't register.
In the settings there are two options , one for login page which is turned off and one for register page which is turned on. We would like to leave it on to help prevent spam bots from registering.
I am using current versions of WP/BP and the membership plug in. See screenshot at the bottom where the captcha is located. Thanks.