One of the joy’s of owning a Nexus device, other than getting the latest OS before everyone else, is the fact that Google offers modders more access and control of these devices in the way of publicly downloadable factory images.
Although the Nexus range of devices aren’t so easy to get hold of in the run up to the holidays, Google have stayed true to the spirit of Nexus and have made factory images available for the Nexus 4, Nexus 7 and Galaxy Nexus range of devices.
To get the 4.2.1 factory images simply head over to the Google factory image page, download the image you want and start tinkering, hacking and modding away, safe in the knowledge you can easily restore your device to factory defaults whenever you like.
While this is great news for anyone with a Nexus 4, Nexus 7 or Galaxy Nexus, those users who opted for the “Big Daddy” Nexus 10 won’t be rejoicing just yet as factory images have yet to be made available.
Even though it is fun to hack your Android devices, we recommend only those of you who are completely comfortable with what you are doing attempt to mod your devices. We don’t want you to accidentally brick your Nexus this holiday season.[ Source ]