You can convert KML/KMZ to GPX using online tools like http://www.gpsies.com/convert.do . After that you can use much more tools to do it.
There is desktop application GPS Babel
to convert it.
You can use Darktable and load GPX file to geotag images.
For GNU/LINUX users:
KMZ is a zipped file with KML files. You can create script which will decompress it.
Next you can iterate and covert every KML to GPX using
gpsbabel -i kml -f in.kml -o gpx -F out.gpx.
You can use https://github.com/akwiatkowski/gpx2exif tool to geotag JPEGs.
I have wrote it to geotag my photos using GPX files from GPS device (Garmin eTrex). It is a bit quirky and it is suited to my needs.
As you can see it is not a easy and ready solution, but if you are pro-user you can automate it for yourself.