How do I change the lockscreen wallpaper on XFCE?

I tried installing light-locker and light-locker-settings like someone suggested, but there is still no option to change the lockscreen wallpaper.

  1. Open the LightDM GTK+ Greeter settings app from the apps menu
  2. In the Appearance tab, under Background, click on the rectangle next to Image
  3. Select the wallpaper you want to use and click open
  4. Click Save