When I had Google Fiber installed, the Google Fiber Storage Box shared location, gfiberstorage, appeared on my Mac and Windows PCs, with three folders: Music, Photos and Videos.
In the Photos folder, there is a subfolder named Landscapes, and in the Landscapes folder were eight images.
If you leave your Google Fiber TV paused for awhile, you see scenic images. At first, I did not know where the images came from, until I looked in the Landscapes folder and saw that the images were the same.
To test things, I created a new subfolder in the Photos folder, named custom, and placed a photo in it.
The next time the screensaver appeared, after I had paused the TV for awhile, the photo from the custom folder was included in the screensaver.
I don’t do much with custom screen savers, even on the computer, but it is nice to know where the images are stored, if I ever wanted to change the Google Fiber TV screensaver images.