It was a great question, even though Obama didn't answer it and the press corps laughed. The "Neda video" has brought home for a lot of people the immense power of images to shape public debate, especially where violence is concerned. When it comes to forms of state violence like killing protesters or torturing detainees, suppressing images is suppressing vital information, information that makes concrete for the public what is actually involved in practices that can otherwise sound clinical and basically harmless. (Here at least, Alicia C. Shepard, NPR's champion of vivid writing and of the avoidance of the word "torture," we can agree: "Show, Don't Tell.") Glenn Greenwald and Alice Ristroph both have posted thoughtful pieces about this.
At the same time, I think it's important to be clear about the limits of what images can do in shaping public debate. As Philip Gourevitch wrote in the NYT last month,
Photographs cannot show us a chain of command, or Washington decision making. Photographs cannot tell stories. They can only provide evidence of stories, and evidence is mute; it demands investigation and interpretation.