How to add Captcha at Login Page without any Plugin

Hai

I’m facing lot of failed login attempts in my site Geek Dashboard from last couple of months. Someone is trying hard to hack in to the site. I installed a plugin to show captcha in Login page and it worked like a charm. Now failed logins is greatly reduced.

I don’t want to use more plugins, so i just wanna know whether it is possible to add captcha in login page with out using any plugins

Thanks