Sometimes, requirements from people you work with can help you explore things you may never have. I have developed a few websites on WordPress and I never bothered to think about changing the logo displayed on WordPress login page ever.
But while developing a website using WordPress for a client, they wanted to display their own logo on the login page instead of the default WordPress logo. Since I don't believe in "re-inventing the wheel" and since WordPress is well supported by tons of plugins from developers, I thought there would be a plugin for that too. And lo, there is. If you would like to customize the login page or remove the WordPress logo displayed in the login page and replace it with your own or organisation's logo, you can easily do so with plugins available.