Make JPEG readable by GR III?

Felix E Klee wrote:

You need one photo taken with the camera, here:

R0000349.JPG

For testing, if you don't have an existing image, create one (can be any aspect ratio):

convert -size 2000x1000 radial-gradient:red-blue TEST.JPG

Then convert that image:

INPUT=TEST.JPG

OUTPUT=A0000001.JPG # DCF compatible

THUMBNAIL=THUMB.JPG

ORIGINAL=R0000349.JPG # taken with the camera

convert -sampling-factor 4:2:2 $INPUT $OUTPUT

exiftool -TagsFromFile $ORIGINAL -all:all -unsafe -XML:All -JFIF:ALL= $OUTPUT

convert $INPUT -resize 160x120 -background black -gravity center -extent 160x120 -sampling-factor 4:2:2 $THUMBNAIL

exiftool "-ThumbnailImage<=$THUMBNAIL" $OUTPUT

To set the orientation of the image, add another step:

ORIENTATION=1 # 1 = 0°, 3 = 180°, 6 = 90°, 8 = -90°

exiftool -Orientation=$ORIENTATION $OUTPUT

Finally, put $OUTPUT into a DCF compatible path on your camera.

Make sure that the number in the file name is unique on the card, or else the camera may be confused. For example, if there is A0000001.JPG and B0000001.JPG on the card, then my Ricoh GR III displays neither of the images.

This solution can be scripted. In my case I want to make dozens of maps of Hong Kong readable by the camera.

Felix. I have been trying to do this following your instructions. It all works perfectly - until I substitute a real image file

convert -size 2000x1000 radial-gradient:red-blue TEST.JPG

If I use a found jpg image from the internet I get a file that cannot be read by the camera.

I have tried putting the image file in the command line instead of the 'radial-gradient:red-blue', and I have also tried simply renaming an image to TEST.JPG. Neither methods work - both fail the same way.

So, I then tried to make a simple image (hand-drawn cross on white) in OS X Graphic Converter with no exif data in the saved jpg file (as I thought maybe there was some data in the found image files it did not like) and the camera can read it, but only shows a low-res thumb and cannot zoom in.

Can you describe the process that substitutes a real image file for the red-blue gradient please?