How do you change the user picture on the login screen?

[Federico Leoni]

Gentlemen,

as far as I understand Aere is asking for a way to change the USER
IMAGE, not the wallpaper...
To change the user picture you need to create a file called

.face

in jpg format and without any extension then put it on your home
folder. The image need to be a square one (I use 400x400 pixel). Don't
forget the dot.
Png format doesn't work on LightDM but works for GDM. Tested on both
13.04 and 13.10. Don't know if there is a gui for this, normally the
file isn't present on Lubuntu home folder.

F.