I got a Opengl example contain “#include <gl/image.h>”.
I’m using RedHat Linux 9.0. and how I can install this header.

Sounds like Paul Haberli’s image libs that basically load SGI images (and a few others) into packed memory arrays for texture loading.

Remove the include & see what happens. If it doesn’t work look for a 3rd party image loader that does the equivalent but you need to start looking at the calls not just the headers.