Grub2 Splashimage

GRUB 2's splash image/background capability is greatly enhanced over its predecessor, GRUB 0.97. This page provides information on how to add a background image, change font colors and resolutions on the GRUB 2 menu without using a theme. The developers have created a set of compatible background images available as a package download but GRUB 2 accepts a variety of popular image formats. The user may choose any compatible image to use on the GRUB 2 menu.

sudo apt-get install grub2-splashimages

sudo update-grub 

Once installed, the images are located in the /usr/share/images/grub folder. 

1. GRUB_BACKGROUND setting in /etc/default/grub
2. First image found in /boot/grub
   • The first image found, in this order: jpg, JPG, jpeg, JPEG, png, PNG, tga, TGA
   • If multiple images of the same extension, alphanumerically.
3. Wallpaper designated in /usr/share/desktop-base/grub_background.sh (if desktop-base installed)
4. WALLPAPER= line in /etc/05_debian_theme * GRUB 1.98 only
   • The default setting is /usr/share/images/desktop-base/desktop-grub.png (the desktop-base package must be installed)
5. Default theme (no image): default_theme colors specified in /etc/grub.d/05_debian_theme

Note: Not all these options are available in GRUB 1.98

source