OK the scenario......
you have multiple users on your system and you have changed permissions on /home/you so every one but you and your group is forbidden access to /home/you .
well now lightdm cant read your .face icon ,,,,, but their is hope.
if you go to /var/lib/AccountsService/icons and add a folder named your user name like this (we will use mine in the example so replace vinny with yours)
then place the ~/.face you were using in it.
now go to
and you will see a .txt file with your user name their already, open it and add the line
so it looks like this
save exit and reboot ,,,,,,,,behold your icon is back 
you will nead to be root so do the "kdesudo dolphin" thing or use your root actions service menus
VINNY
you have multiple users on your system and you have changed permissions on /home/you so every one but you and your group is forbidden access to /home/you .
well now lightdm cant read your .face icon ,,,,, but their is hope.
if you go to /var/lib/AccountsService/icons and add a folder named your user name like this (we will use mine in the example so replace vinny with yours)
Code:
/var/lib/AccountsService/icons/vinny/
now go to
Code:
/var/lib/AccountsService/users/
Code:
Icon=/var/lib/AccountsService/icons/vinny/.face
Code:
[User] XSession=kde-plasma Icon=/var/lib/AccountsService/icons/vinny/.face

you will nead to be root so do the "kdesudo dolphin" thing or use your root actions service menus

VINNY