These images can be used to flash KitKat on your Nexus device but you risk losing all your device data and also make a backup before doing so, you will also need to have unlocked bootloader. Factory images are mostly used when users mess up their pre-loaded firmware while tinkering with it.
Originally announced on October 31, Android 4.4 KitKat brings several improvements and new features to the Android operating system including inbuilt cloud-print support, new keyboard, lock-screen widget improvements, immersive mode, faster multitasking, and better dialler app.
Direct links to download factory images: Nexus 7 2013 (Wi-Fi, 3G/ LTE), Nexus 7 2012 (Wi-Fi, 3G), Nexus 4, Nexus 10. You can also find these links at Google Developers website.
