Multiple images may be specified, in which case one is picked at random. That's a TrueColor BMP3 in Imagemagick, or 24-bit BMP/DIB in Microsoft Paint. The image must be a 24-bit BMP file with a 54-byte header. It's usually very difficult to change the image permanently, but a custom UEFI application may be used to overwrite it during the boot. But downloading and installing it on your computer is where you need to pay attention. When booting on a UEFI-based computer, Windows may show a vendor-defined logo which is stored on the UEFI firmware in a section called Boot Graphics Resource Table (BGRT). The default path is \EFI\HackBGRT\splash.bmp. Using 8oot Logo Changer to change the boot screen is extremely easy. The image path can be changed in the configuration file. The configuration options are described in config.txt, which should be stored in \EFI\HackBGRT\config.txt. On 32-bit machines, use bootia32.efi instead of boot圆4.efi.