My friend asked me whether he could run Slideshow of Photos on Screensaver. First I thought about Shotwell Photo Manager App. It has Desktop Slideshow option but it did not work on Lock screen.
Then I searched for good old xscreensaver utility and installed it as follows:
$ sudo apt install xscreensaver xscreensaver-gl-extra xscreensaver-data-extra
$ sudo apt remove gnome-screensaver
I added xscreensaver to Startup Applications
Then I opened Screensaver Preferences and selected GLSlideshow in Display Mode
then selected Pictures Folder in Image Manipulation/Choose Random image
and it works on reboot.
