I have already installed scrot following the instructions here.  The Windows Manager appears to be Openbox.  
How can I take a screenshot in LXDE using scrot and the Print Screen button on my keyboard?
openbox;lxde;screenshot;raspberry pi
Edit ~/.config/openbox/lxde-rc.xml with your favorite text editor and then, within the existing <keyboard> element, add the following lines:<keybind key=Print>  <action name=Execute>    <command>scrot</command>  </action></keybind>Use the openbox --reconfigure  command to use the new settings. Following the restart, a screenshot will be created in your /home/pi directory every time you press the Print Screen button.  There's also a GUI tool called obkey which can make editing the Openbox config file easier.  You can find it here.  