sudo apt-get install xvfb imagemagick libjpeg-dev
=== capture xvfb , convert to jpeg
/usr/bin/Xvfb :88 -screen 0 960x544x24+32 +extension Composite -nocursor -ac -fbdir ~/ & xlogo DISPLAY=:88 xlogo & sudo apt-get install convert ./Xvfb_screen0 ~/screen.jpg