[Solved] Linux: make screenshot of the virtual screen

Make screenshot on display 1 with the imagemagick

DISPLAY=:1 import -window root screen.png

Source: Xvfb and Firefox headless screenshot generator « Ivan Villareal.

[SOLVED] Running headless on Linux

First, install a VNC server:
sudo apt-get install vnc4server

Next, start and configure the server:
vncserver

At this point, it should ask you to create a password for VNC. Do so, then continue.

Start a VNC screen on screen 99:
vncserver :99

If that goes through alright, then kill the screens created. (For me, when I ran vncserver for the first time, it created a screen at :1, so we'll kill both of the screens created)
vncserver -kill :99
vncserver -kill :1

Done. Now, it "just works."

Source: http://forums.adobe.com/thread/740482

[SOLVED] Linux: resize all images via console

Just install ImageMagick if you dont have it yet

sudo apt-get install imagemagick

Resize all JPG files in to desired size

mogrify -resize 640x480 *.jpg

Source: http://www.baptiste-wicht.com/2010/09/tip-batch-resize-images-on-ubuntu-linux/