genwallpaper.py

import os
import xml.etree.cElementTree as ET

wallpapers = ET.Element("wallpapers")
for root, dirs, files in os.walk(os.path.expanduser("~/Pictures")):
	for file in files:
		if (file.lower().endswith(('.png', '.jpg', '.jpeg'))):
			wallpaper = ET.SubElement(wallpapers, "wallpaper")
			wallpaper.set("deleted", "false")
			name = ET.SubElement(wallpaper, "name")
			name.text = file
			filename = ET.SubElement(wallpaper, "filename")
			filename.text = os.path.join(root, file)
			options = ET.SubElement(wallpaper, "options")
			options.text = "zoom"

tree = ET.ElementTree(wallpapers)
tree.write(os.path.expanduser("~/.local/share/gnome-background-properties/gnome-backgrounds.xml"))