Pardus fellow craft
It's quite easy to change your user image. Just do the following:
Just open Tasma (Pardus >> Tasma)
Then go to system and click the Login screen option
Then become administrator using the Administrator Mode button on the bottom of the screen.
After click the users tab
Then on the right side of the screen you see a part called User Pictures (or something similar, i'm using pardus in dutch)
There set the user to your own username and then click the picture.
Now choose the image you want.
When finished click the apply button to apply the settings.