Customise your ADFS login experience
There are many elements on the ADFS login page that can be customised. For a complete guide, look here!
My recommendation is to have the important part of the left side picture(the big one) – in the upper left corner, so it will be visible even on low resolution displays.
As far as I know, there are no way to customise the login image in the previous step, that is on the “portal.microsoft.com” – since that is a MS server.