How to take a snapshot of a video

Download VLC Media Player http://www.videolan.org/vlc/index.html & open your media file with it.

If you want to take a snapshot, when you watch a film in VLC, press down the hot-key for snap shooting. The pre-defined hot-keys is in

MAC OS X: Command+Alt+s,
Windows,Linux, and Unix: Shift+s.

If you want to change the hot-keys go to Preferences → Interface → Hotkeys and set Take video snapshot. Then write the hot-keys you want.
After you have tacked a snapshot you may want to see it.

In Windows you can find it at:  My Documents\My Pictures\
In MAC OS X:   Desktop/
In Linux and Unix:   $(HOME)/Pictures/