Hi
Netinstall exist for mac oS 10.6 (Apple source). Mac OS X 10.6 Server Admin: Création d’images NetInstall
And other source: Create a Leopard to Snow Leopard Upgrade NetInstall Image
Here with the newest driver and security update it runs smoother than ever in High Sierra ..
1GB Security Update, even the 2011 MBP with SSD runs significantly better... Already had given up on it.
I can not find the exact information, Sorry
what I know is that on old Mac 10.6 and 10.7, and maybe even more as I've seen, you need OS X Server.app to create the disk image because the old system does not get System Image Utility.app like in High Sierra
System /Library /CoreSerices/Applications/ System Image Utility.app