Using this tool you can create the following:
You need image magick core to be installed. Then just do:
$ waf configure build
Setting top to : /home/usr/proj/normalmap
Setting out to : /home/usr/proj/normalmap/build
Checking for 'gcc' (c compiler) : /usr/bin/gcc
Checking for program pkg-config : /usr/bin/pkg-config
Checking for 'MagickCore' : yes
'configure' finished successfully (0.044s)
'clean' finished successfully (0.004s)
Waf: Entering directory `/home/rich/proj/normalmap/build'
[1/3] c: src/normalmap.c -> build/src/normalmap.c.1.o
[2/3] c: src/main.c -> build/src/main.c.1.o
[3/3] cprogram: build/src/normalmap.c.1.o build/src/main.c.1.o -> build/normalmap
Waf: Leaving directory `/home/rich/proj/normalmap/build'
'build' finished successfully (0.179s)
The binary can then be copied from build/normalmap.
The algorithm to compute the normal map is taken from the gimp normal map plugin. (https://code.google.com/p/gimp-normalmap/). I found no simple way to create such a normal map via command line.
Like the gimp normal map plugin GPLv2