List all graphic image files with find?

This should do the trick

find . -name '*' -exec file {} \; | grep -o -P '^.+: \w+ image'

example output:

./navigation/doc/Sphärische_Trigonometrie-Dateien/bfc9bd9372f650fd158992cf5948debe.png: PNG image
./navigation/doc/Sphärische_Trigonometrie-Dateien/6564ce3c5b95ded313b84fa918b32776.png: PNG image
./navigation/doc/subr_1.jpe: JPEG image
./navigation/doc/Astroanalytisch-Dateien/Gamma.gif: GIF image
./navigation/doc/Astroanalytisch-Dateien/deltaS.jpg: JPEG image
./navigation/doc/Astroanalytisch-Dateien/GammaBau.jpg: JPEG image

The following suits me better since in my case I wanted to pipe this list of files to another program.

find . -type f -exec file --mime-type {} \+ | awk -F: '{if ($2 ~/image\//) print $1}'

If you wanted to tar the images up (as someone in the comments) asked

find . -type f -exec file --mime-type {} \+ | awk -F: '{if ($2 ~/image\//) printf("%s%c", $1, 0)}' | tar -cvf /tmp/file.tar --null -T -