I modified lightdm-gtk-greeter.conf, all options took effect except the background image. The background is displayed in black color.
The image path is valid and the right is 755. There is not log files under /var/log/lightdm.
The content of the conf file is:
Same here. Looks like https://bugs.launchpad.net/lightdm/+bug/1086199
Will investigate this tomorrow, it's too late today.
This alpha channel bug has been fixed in the development branch (1.6). The current version from this branch (1.5.1) is available in the AUR.
The bug, as far as I am aware, will not be fixed in the stable branch (1.4). To resolve this, open the image in Gimp and add an alpha channel.
OK, the lightdm-gtk3-greeter-devel package has resolved that. Thanks.