According to their main page, all you have to do is add 4 lines of code. My guess is that you'd have to check the documentation that comes with recaptcha and see what it is that you have to do exactly. Then in vShare's admin panel, my guess is that you would disable the captcha with signup and in the signup.tpl or login.tpl (not sure which one) you'd stick in this recaptcha code. Just a guess.