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?
Had the same problem... Edited pictures were not recognised by the Canon Selphy CP1200. Here's what worked for me. When using GIMP, proceed to export the picture as a jpg. After clicking on the "EXPORT" button, another menu pops up. Hit the "+" on the "ADVANCED OPTIONS" to bring up more menu options. I removed the check marks from the "optimize" and "progressive" options, removed any comments in the comment section and changed the "DCT Method" from Integar to Floating-Point. Then pressed the "export" button. Pic then worked with the cp1200. Don't know which of these options or combination of these options causes the pics to work, but takes half a sec to do 'em all instead of mucking around to find out which options solved the problem.
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.