Hi again,
Thanks for your feedback.
We only supported to enable captcha on registration so you can go to JM Jobmonster > Settings >Member> Enable Captcha on Registration.
For the login form, we think that you don't need to install a third-party plugin because when using captcha on the register form, it is absolutely safe. Only users who have an account on your site have a right to get access to your site. Thus, it is not necessary to add a captcha in the Login form.
If you still want to have a captcha on Login form, we think that you should add an additional option which allows you to enable captcha instead of using a third-party plugin.
Best Regards,
NooTheme