How I do one of many "greeters" that I use by editing 2 files, their are more options to use then what I use myself, I am happy with what I use for my machines
/etc/lightdm/lightdm-gtk-greeter.conf[greeter]
background=/disks/disk3part1/siduction/kong bookmark icons/wallpaper-485031.resized.png
#show-language-selector=true
theme-name=Adwaita
#font-name=
xft-antialias=true
#xft-dpi=
xft-hintstyle=hintfull
xft-rgba=rgb
default-user-image=/disks/disk3part1/siduction/kong bookmark icons/piper_avg.png
show-clock=true
clock-format=%H:%M
/usr/share/lightdm/lightdm.conf.d/01_debian.conf[SeatDefaults]
greeter-session=lightdm-greeter
greeter-hide-users=false
session-wrapper=/etc/X11/Xsession
This
/usr/share/kde4/apps/lightdm-kde-greeter/themes/and this
/etc/light/lightdm-kde-kde-greeter.conf Does not exist on my system