Wallpaper slideshow without manual intervention

I wanted to create a desktop wallpaper slideshow with my own set of images as described in this answer using shotwell but faced certain problems - once photos are selected from shotwell for slideshow ; it continues using even those images which have been deleted manually from the specified folder after selection of photos - similarly when photos are added they aren't automatically picked up for slideshow In short How to set up the slideshow in such a way that photos are automatically picked or removed ?I will prefer scripts over any extra apps if possible or apps if they are from well known authentic sources .