About 7 years ago I posted here how to create a boot logo:
Those tips were very useful, but it was missing an important step, how to convert your image to only 224 colors needed by the Linux kernel?
Easy, use the tools from netpbm package:
$ sudo apt-get install netpbm $ ppmquant 224 original_image.ppm > boot_logo_224.ppm $ pnmnoraw boot_logo_224.ppm > boot_logo_ascii_224.ppm
Now you just need to follow the tips from previous post to get it working.