If logging into ADFS is something that your users have to do on a daily basis, why make it a boring affair?
I wrote a PowerShell Script that randomly chooses an image from a specified directory and sets it as the Illustration for the login page.
It has the ability to select images from different folders based on a date range that you configure, so you can use it for anything from birthdays to themes for certain seasons or special events.
To automate it you just need to make a scheduled task.
Also, if you have any issues feel free to raise a bug or better yet fork the rep'o make the change and then make a pull request!