Adding thumbnail images does not seem to work

[SimonKravis]

I would like to store the full original image as a thumbnail as I propose to modify it but would like to be able to recover the original. If I run exiftool as below

C:\Users\simon\Pictures>exiftool -ThumbnailImage="IMG_0444.JPG" "IMG_0444.JPG"
Warning: [Minor] Not a valid image for Olympus:ThumbnailImage
    0 image files updated
    1 image files unchanged


If I try to extract the thumbnail after applying as above with

exiftool -b -ThumbnailImage IMG_0444.jpg > IMG_0444_thumb.jpg

I get an empty file. What am I doing wrong?

[Phil Harvey]

This is common mistake 5c.

- Phil

[SimonKravis]

This code worked - needed to replace = with <= and enclose the first param in double quotes as below

exiftool "-ThumbnailImage<=IMG_4049.JPG"  IMG_4049.JPG

Thanks Phil