Debian Linux logo
1 Create your own logo file
Create your logo in a .png format (logo.png), and run the following to convert it to a 224 colors PPM formatted image file named logo_linux_clut224.ppm: Host PC
$ sudo apt-get install netpbm $ pngtopnm logo.png | ppmquant 224 | pnmnoraw > logo_linux_clut224.ppm
2 Replace the default logo file in the Linux source
2.1 Using the Linux source code directly
Follow the "Build Linux from source code" guide to get the Linux kernel source tree.
Copy your logo_linux_clut224.ppm file to ~/var_mx6ul_dart_debian/src/kernel/drivers/video/logo/logo_linux_clut224.ppm overwriting the original logo.
Configure your kernel and enable the default logo instead of the Variscite logo: Device Drivers -> Graphics support -> Bootup logo -> Standard 224-color Linux logo (Symbol: LOGO_LINUX_CLUT224)
If you want to create a different configuration for your own logo rather than overwriting the default one, you can look at this commit which adds the Variscite Linux logo to our kernel, and make a similar patch of your own.
2.2 Build the kernel
Followto build a newly created kernel and your logo should be up while booting new Debian Linux.