How to Take a Screenshot in Linux With the Terminal (scrot)
To install scrot (on Ubuntu) type:
sudo aptitude install scrot
To take a screenshot in Linux from the terminal with scrot type:
scrot MyScreenshot.png
http://tips.webdesign10.com/how-to-take-a-screenshot-with-ubuntu-linux
http://www.itnewb.com/tutorial/Using-Scrot-the-Screen-Shot-Command-Line-Utility-for-Linux