You can customize the login page by adding a logo or a background image of your choice. You need to be an administrator to perform this task.
Go to Settings > Account > Look & feel.
To change the background image:
Hover your mouse over the image under Set background image for your account login page.
Click the plus icon and upload the new image.
The image should be at least 1500 pixels in order to ensure high quality.
To change the existing account logo or the account login logo, hover your mouse over the image under Set account logo and Set account login logo. Click the plus icon and upload the new image.
The logo on the login page should be at least 200x200px.
Save your changes.