Fastest method for screen capturing on Linux

Question

This question is similar to this one

Fastest method of screen capturing

but for linux/X11.

To be more specific, i need a method to capture the pixel

Answer 1

I'd grab the sources for gnome-screenshot, or some other existing open-source tool, and figure out how they do it.

You can find the sources Ubuntu uses here: http://packages.ubuntu.com/quantal/gnome-screenshot

But, don't forget to check the license before you cut and paste large sections of code!