Charles Paul Freund is a senior editor of Reason, a monthly magazine on politics and culture, who has written extensively on the political manipulation of culture, the ideological use of imagery and language, modern techniques of persuasion and the process of disseminating ideas.
In this LA Times op-ed, which is a must read in its entirety, Mr. Freund makes the following salient point in comparing the responses to the recent images of the Abu Ghraib prison and the beheading of Nicholas Berg:

The Abu Ghraib pictures reveal American soldiers humiliating their prisoners in a sadistic manner (in some images, the Americans are actually smirking). It’s a painful sight because it is cruel on its own terms (we don’t even know whether the terrorized individuals are actually guilty of anything) and because we regard such sadism as unworthy of our image of ourselves.
By contrast, Zarqawi intentionally videotapes and distributes his bloody atrocity; the literal slaughter of an innocent is offered as an example of his righteousness. For Zarqawi, the question of unworthiness simply never enters the calculation; that the action is inhuman is its point.
Shameless brutality of this degree has the power to transform the shame of Zarqawi’s enemies. Zarqawi has reminded his enemies that, unlike him, they are at least capable of shame.
Zarqawi’s righteous snuff movie is an act of lunacy, a gift to his enemies, and, one hopes, an unwitting suicide note.

Hat tip to Virginia Postrel for the link to Mr. Freund’s timely piece.