Visual images have been a central component of propaganda for as long as propaganda has been produced. But recent developments in communication and information technologies have given terrorist and extremist groups options and abilities they never would have been able to come close to even 5 or 10 years ago. There are terrorist groups who, with very little initial investment, are making videos that are coming so close to the quality of BBC or CNN broadcasts that the difference is meaningless, and with access to the web they have instantaneous access to a global audience. Given the broad...