If you are referring to the "splash screen" picture that appears as the OS is loading, a search for "
change Fedora splash screen" will turn up a number of items. It appears that it cannot be done though System Settings, but can be done by editing a configuration file.
In Linux, the term "boot image" commonly refers to the version or "image" of the Linux kernel that starts when you boot the system.
Oh, and welcome to LQ.
How to change boot image?
