efi boot screen background grub

this might be a mute question, but how to set up a grub background using grub efi in slack?

the in the default/grub is not working.
it says it pics it up but it never shows.

Code:$ update-grub
Generating grub configuration file ...
Found background: /boot/efi/EFI/slackware-14.2+/Andreea-Munteanu-001.jpg
Found linux image: /boot/vmlinuz-huge-4.19.81
Found initrd image: /boot/initrd.gz
Found linux image: /boot/vmlinuz-huge
Found initrd image: /boot/initrd.gz
Found linux image: /boot/vmlinuz-generic-4.19.81
Found initrd image: /boot/initrd.gz
Found linux image: /boot/vmlinuz-generic
Found initrd image: /boot/initrd.gz
Found Windows Boot Manager on /dev/sdb1@/EFI/Microsoft/Boot/bootmgfw.efi
Found unknown Linux distribution on /dev/sdb7
done