Impossible!
Google home app is the only app you can use to control google chromcast. I was trying to change the backdrop photos on my chromcast and when I google how to do it google tells you to use the chromcast app, but no such app exists. When you go in to the google home app and try to change the backdrop photos it sends you to backdrop settings and edit backdrop, both those send you to the exact same place. Only you can NOT add your own photos to chromcast backdrop from the google home app you have to add them from google plus app but good luck finding that information anywhere! Why not make the app easy to use and make it so you can add your own photos to chromcast from one app not have to use two different apps? Keep it simple stupid!
prokevin92 about
Google Home, v1.26.812