In order to create NetInstall image please proceed with the following
Download Install OS X application from the Mac App Store
Copy it into Applications folder, if it's not already there.
In Finder choose Go > Go to folder... > /System/Library/CoreServices/ > Ok and run System Image Utility.app
- NetInstall image option should be enabled. Install OS X application should be available as a source for creating NetInstall image. Select it and create new image.