Backdrop should be the default screensaver on your Android TV device.
I like this one: https://play.google.com/store/apps/details?id=com.gmail.ek9852.photoalbum I point it at my NAS folder but it also supports online sources.
Yes, it's daydream compatible meaning you can set it as screensaver in Android settings. It has some really nice effects and animations.
I really like this one. https://play.google.com/store/apps/details?id=com.furnaghan.android.photoscreensaver