We took a picture with a digital camera, and used GNU Image Manipulation Program (GIMP) to remove some stuff in the background, and tried to print it on our Canon Selphy CP1200. The print failed, and the manual says "images may not be displayed or printed correctly if they have been edited on a computer". What does it take to get the Selphy to print an edited JPG?
You might try Export (in Gimp) with unchecked "Save EXIF data" and "Save XMP data" Advanced options (see here).
Then copy the original EXIF info from the untouched camera JPEG onto the exported image using ExifTool:
exiftool -TagsFromFile srcimage.jpg "-all:all>all:all" targetimage.jpg
srcimage.jpg is the original camera JPEG
targetimage.jpg is the Gimp exported JPEG without EXIF and XMP metadata
I don't have such a printer so can't confirm that it will work.
Exiftool copy metadata example copied from here.