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.
Fingerprint GUI is an application providing fingerprint-based authentication on Linux desktops. It features a simple GUI for fingerprint management and a PAM module. It is based on the libfprint library. It enables recording and checking of fingerprint data and allows login and authentication of users by their fingerprint using a fingerprint scanner. Additionally, you may install the bundled non-free libbsapi library. In this case Fingerprint GUI will automatically support all fingerprint readers manufactured by UPEK, Inc.
Fingerprint GUI is free software. You can use, modify, copy and distribute it under the terms and conditions of the GNU General Public License (GNU GPLv3). The safety and reliability of the fingerprint-recognition depends very much on the hardware used, the associated device drivers and the software used to verify the biometric data. According to the current state of the art fingerprint recognition for security-critical applications is only limited suitable. More information about safety of fingerprints can be found here. For the list of fingerprint readers supported by libfprint check this link.


Supported readers (run command lsusb to find out the ID of your reader)
045e:00bb08ff:168308ff:258008ff:268d
045e:00bc08ff:168408ff:266008ff:268e
045e:00bd08ff:168508ff:268008ff:268f
045e:00ca08ff:168608ff:268108ff:2691
0483:201508ff:168708ff:268208ff:2810
0483:201608ff:168808ff:268308ff:5501
05ba:000708ff:168908ff:268408ff:5731
05ba:000808ff:168a08ff:2685138a:0001
05ba:000a08ff:168b08ff:2686138a:0005
061a:011008ff:168c08ff:2687138a:0008
08ff:160008ff:168d08ff:2688147e:1000
08ff:166008ff:168e08ff:2689147e:2016
08ff:168008ff:168f08ff:268a147e:2020
08ff:168108ff:250008ff:268b147e:3001
08ff:168208ff:255008ff:268c1c7a:0603
147e:1003147e:3000147e:1002147e:2015
147e:5003147e:5002147e:1001

To install Fingerprint GUI in Ubuntu 15.04 Vivid/14.10 Utopic/14.04 Trusty/12.04 Precise/Linux Mint 17.1/17/13 open Terminal (Press Ctrl+Alt+T) and copy the following commands in the Terminal:
That's it
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