As eternal said, (i think), the captcha is based on failed attempts to login, yeah?
So if you successfully logged into an account at a set interval, the captcha wouldnt appear, and you wouldnt need to bypass it.
Or i could be missing the point entirely! I know nothing of cracking/hacking/programming.
Depends on how many times you login / failed attempts.
If you plan on having em login directly to the homepage and only needing to login once then thats pretty easy.
Otherwise you need a exploit (alternative) way of logging in.