Question: So, I recently upgraded my Xubuntu to 13.04, and afterwards I noticed that there is now a picture of me on the lightdm login screen. I have no idea where this picture came from, I don't remember it being taken.

I guess it was asked for when I set up the account. Long time ago now.

Anyway, I was wondering whether it was possible to change this picture... I don't really like it.

Answer: 
Take a **JPEG** image of your choice. Move/copy it to Your Home folder. Rename it to ".face". Yes, a dot-file without extension. Log out, and You should see it!

It should be JPEG and also a square. PNG will not be shown (it works for User Manager, but not for LightDM login, unfortunately). Image of irregular dimensions will get streched.

This works for me on Xubuntu 13.04. Good luck!
Try System Settings - User Accounts. Click on the grey head (or the thumbnail ) that's shown above 'Account Type'. There you can change it. 

But...a default Ubuntu 13.04 installation will not show a picture of you in the lightdm login screen.

There's information on [Help Ubuntu](https://help.ubuntu.com/13.04/ubuntu-help/user-changepicture.html) and [on this ArchWiki page](https://wiki.archlinux.org/index.php/LightDM) on how to customize lightdm.

You need to edit the 

```
/etc/lightdm/lightdm-gtk-greeter.conf

```

This is how a fresh installed lightdm-gtk-greeter.conf file looks like:

```
#
# background = Background file to use, either an image path or a color (e.g.     #772953)
# theme-name = GTK+ theme to use
# font-name = Font to use
# xft-antialias = Whether to antialias Xft fonts (true or false)
# xft-dpi = Resolution for Xft in dots per inch (e.g. 96)
# xft-hintstyle = What degree of hinting to use (hintnone, hintslight, hintmedium, or hintfull)
# xft-rgba = Type of subpixel antialiasing (none, rgb, bgr, vrgb or vbgr)
# show-language-selector (true or false)
#
[greeter]
background=/usr/share/backgrounds/warty-final-ubuntu.png
theme-name=Ambiance
font-name=Ubuntu 11
xft-antialias=true
xft-dpi=96
xft-hintstyle=slight
xft-rgba=rgb
show-language-selector=true

```

file.