I know this post is old, but here is a link especially if one wants to take a picture from the terminal process or shell or bash script, using gst Gstreamer.http://wiki.laptop.org/go/Programming_the_camera
From the web page, I haven't verified that it works or is current:
First, let's see the quickest way we can capture a still image from the camera--using a GStreamer command-line tool:
gst-launch-0.10 v4l2src ! ffmpegcolorspace ! pngenc ! filesink location=foo.png
It goes on to explain what is happening, how to do it with python, and more.