Just something I have just tried to do, is set the screensaver in Emby Theatre. Settings > General > Display > Screensaver
The options are: None, Logo or Backdrop.
Would it be possible to use the Photos Library?
I am configuring to replace my old Windows 7 MCE box, the Screen saver of our family photos comes up a lot while the TV is left on.
We often find ourselves sitting and watching at times.
It's a really nice way to just view random family images.