There’s no clear, reliable way from the provided answers to guarantee that a Fujifilm X camera will display an arbitrary computer-generated image. Many cameras expect specific DCIM folder structure, filenames, EXIF, and sometimes thumbnail data, and Fuji may reject files that weren’t created in-camera.

The practical workaround suggested is simple: create your “safe to format” graphic on your computer, display it full-screen, and photograph that screen with the Fuji. Because the camera created the file itself, it will be stored in the expected format and location and should display normally in playback.

So while it may be possible to mimic the exact metadata and thumbnail structure, it’s not a dependable method unless you reverse-engineer Fuji’s requirements. Taking a photo of the message is the safest and easiest solution.