I found some images on the internet about some GRUBs with a background image, I would like to do something like that too, but how? I have GRUB2.
The Ubuntu wiki has a detailed guide. First, you need to make sure the image is in the right format: a 256-color non-indexed RGB JPEG. GRUB checks a number of different places for background settings, and it varies by version; here is the first place checked for two versions:
1.99 and up