On my Roku TV you can easily upload photos to use as your Screensaver or to just view, through the app. But I can't find a way to do this on my Google tv. The Google photos app can be pulled up using voice commands but it cycles through all of the photos uploaded randomly and you have no control.
I can select which photos to show in screensaver settings on my Sony android tv. Generic photos, Google photos, specific Google photos album, etc.
Is there a Roku sub? Maybe there is a better place to ask. I have no idea what the Roku interface looks like
Google Play store. TV screen saver it's free and basic. There is better ones. If you want more control. I'm thinking slideshow for Google photos is the one you might want to look into. It offers an app purchases I don't know what the price is I've never used it. Hope that helps
Build a photo album in Google Photos, on the stand alone Google Photos app or website. Then using the Screen Saver settings on the Android/Google TV, I think it's under the "daydream" submenu, you can pick that album. It SHOULD work, but sometimes Google will still decide you want to see generic landscapes, graffiti, and space shots.
There have also been instances where I cannot get specific albums to show up as selectable. I wanted scans of Where's Waldo books to be my screensaver, but it will not work no matter what I try. I have no idea why.
Try the Google Home app