How to setup face_recognition ROS (Indigo)

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I am using Indigo on Ubuntu 14. My camera is Asus Xiton Pro.

I have downloaded and setup the basic environment of face recognition package with success. My Fserver and Fclient are running. I am not able to understand how I train the program to recognize new faces and add them to the train.txt

When I try to run 'rosrun usb_cam' node, it throws an error Cannot identify '/dev/video0'. Then I tried "ls -al /dev/video0" the output is 'ls: cannot access /dev/video0: No such file or directory'.

Could someone please guide me to setup this face recognition environment.

Many thanks in advance