Replace `WinPE.jpg` in the WinPE media source folder
Keep the same filename: `WinPE.jpg`
Keep the same image format and dimensions if required by your WinPE build
Copy the new `WinPE.jpg` to the appropriate `WindowsSystem32` or custom branding folder in the WinPE image source
If the image is inside the boot image, mount the `boot.wim`
Edit the mounted image files and replace the existing `WinPE.jpg`
Commit the changes to the WIM
Rebuild the bootable WinPE media
Test the updated WinPE background by booting the new media
