  The application of psychophysiological measures in human-computer interaction
is a growing field with significant potential for future smart personalised
systems. Working in this emerging field requires comprehension of an array of
physiological signals and analysis techniques. An important aspect in measuring
psychophysiological variables in real-world settings is the invasiveness of the
measurement setup. Video is a signal which can be captured from a distance
without interrupting the subject. Furthermore, the advancements in camera
technologies enable detecting a growing variety of psychophysiological
phenomena from a video signal with an increasing accuracy. This paper aims to
serve as a primer for the novice, enabling rapid familiarisation with the
latest core concepts. We put special emphasis on everyday human-computer
interface applications to distinguish from the more common clinical or sports
uses of psychophysiology.
  This paper is an extract from a comprehensive review of the entire field of
ambulatory psychophysiology, including 12 similar chapters, plus application
guidelines and systematic review. Thus any citation should be made using the
following reference: B. Cowley, M. Filetti, K. Lukander, J. Torniainen, A.
Henelius, L. Ahonen, O. Barral, I. Kosunen, T. Valtonen, M. Huotilainen, N.
Ravaja, G. Jacucci. The Psychophysiology Primer: a guide to methods and a broad
review with a focus on human-computer interaction. Foundations and Trends in
Human-Computer Interaction, vol. 9, no. 3-4, pp. 150--307, 2016.
