Gnome slideshow

gistfile1.xml

<?xml version="1.0" ?>
<background>
	<static>
		<!-- Duration in seconds -->
		<duration>120.0</duration>
		<file>/home/ruben/Pictures/Wallpapers/file-1.jpg</file>
	</static>
	<transition>
		<!-- Duration of the transition in seconds, default is 2 seconds -->
		<duration>0.5</duration>
		<from>/home/ruben/Pictures/Wallpapers/file-1.jpg</from>
		<to>/home/ruben/Pictures/Wallpapers/file-2.jpg</to>
        </transition>
	<static>
		<!-- Duration in seconds -->
		<duration>120.0</duration>
		<file>/home/ruben/Pictures/Wallpapers/file-2.jpg</file>
	</static>
	<transition>
		<!-- Duration of the transition in seconds, default is 2 seconds -->
		<duration>0.5</duration>
		<from>/home/ruben/Pictures/Wallpapers/file-2.jpg</from>
		<to>/home/ruben/Pictures/Wallpapers/file-1.jpg</to>
        </transition>
</background>

mis-wallpapers.xml

<?xml version="1.0" encoding="UTF-8"?>
<!-- Place this file in $HOME/.local/share/gnome-background-properties -->
<!DOCTYPE wallpapers SYSTEM "gnome-wp-list.dtd">
<wallpapers>
	<wallpaper deleted="false">
		<name>Mis wallpapers</name>
		<!-- The next bit references the other file -->
		<filename>/home/ruben/Pictures/Wallpapers/miswallpapers.xml</filename>
		<options>zoom</options>
	</wallpaper>
</wallpapers>

Gist to set Gnome to display a custom slideshow.

Adding a new image to the slide show would only need to add a new and section for it.