How to configure a video4linux loopback device

I am writing an application which is based on Motion . Motion allows me to define a video4linux loopback device: # Output images to a video4linux loopback device # The value '-' means next available (default: not defined) ; video_pipe value # Output motion images to a video4linux loopback device # The value '-' means next available (default: not defined) ; motion_video_pipe value Motion already accesses the webcam to detect motion, now I would like to access images of the webcam, too. I think the loopback device is the right thing to do this. But what do I have to do exactly? Do I have to configure another(?) video4linux device and add it in the configuration? Motion offers documentation about this topic. But I find it hard to get starting, as I am still troubled with how the whole architecture is working.