Grub Customizer doesn't change image background

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http://askubuntu.com – I use the latest version of Grub Customizer (3.0.2) and Ubuntu 12.04. On "appearance settings" I changed the background image and the font, but once I reboot the system they don't appear on grub, there's always the default ubuntu background image and the font seems a bit changed but not very well... Why? I tried to resize and crop the image as described here: Why can't I see the image changed with GRUB Customizer? but it doesn't work in any case. On /etc/default/grub: # If you change this file, run 'update-grub' afterwards to update # /boot/grub/grub.cfg. # For full documentation of the (HowTos)