In past there was a way to unlock Linux using face detection method but that is no longer available and maintained by anyone. Another great way to get privileges on your system is Fingerprint, which means you don't have to type password each time you login in to your system or run sudo/su/gksudo command, simply place your finger to your fingerprint device and rest of the process will be automated. Since I don't own any fingerprint device, so I can't tell you how well this method work but looking at developer site this application seems promising and stable by all means, this project is alive since 2008 and still getting updates from developer and application is open to any kind hack/test by anyone then submit bug to developer to fix.
