If you ever want to randomly change your wallpapers every few minutes, hours or whatever, I just made a script to do just that. You can find it here.
This script will at regular interval select a random file within the specified directory and use the specified command to use it as a wallpaper. For example if you want to change your wallpaper every 10 minutes with a picture in ~/Pictures/wallpapers.
wp-random.sh 600 ~/Pictures/wallpapers/ feh --bg-scale
Note that we use feh here to setup the wallpaper, but you can use any command you like.
You can use SIGUSR1 to redraw the current wallpaper (for example if you just enabled the VGA output and the background needs a redraw), or SIGUSR2 to force the selection of another wallpaper:
WP_RANDOM_PID=$(cat /tmp/wp-random_$DISPLAY.pid)
# Redraw current wallpaper
kill -SIGUSR1 "$WP_RANDOM_PID"
# Select another wallpaper
kill -SIGUSR2 "$WP_RANDOM_PID"