File lxqt-lightdm-greeter.conf of Package lxqt-lightdm-greeter-branding-openSUSE

# lxqt-lightdm-greeter.conf
#
# General configuration
# 
# greeter-background = /path/to/background/image to set a background image for the login screen
#
# loginform-offset-x = how far from the left edge of the screen should the loginform be placed. 
#      Can be given in pixels, e.g. loginform-offset-x=60px, or in percentage of screen width, e.g. loginform-offset-x=20%.
#
# loginform-offset-y = how far from the left edge of the screen should the loginform be placed. 
#      Can be given in pixels, e.g. loginform-offset-y=60px, or in percentage of screen width, e.g. loginform-offset-y=20%.

[General]
greeter-background-image=/usr/share/wallpapers/openSUSEdefault/contents/images/1600x1200.jpg
#loginform-offset-x=50%
#loginform-offset-y=50%