(Updated 7 Oct 08)
The manipulation of images for (usually) political and propaganda purposes.
In Simon Singh's Code Book, a history of cryptography, the author's main theme was a constant battle between code makers and code breakers. There appears to be a similar battle rising between image manipulators and image analysts (See bloggers and the various 'fauxtography' incidents over the past few years). This metaphorical trend will probably hold true as digital manipulation and forensics becomes more technical (at the higher technical levels it appears to be more about lots of math and electrical engineering).
The best guys would probably be those that have cut their teeth at Fark, SA, or Worth1000 photoshop contests.
Neal Krawetz is the main researcher on this topic. His blog is here.
Hany Farid is another from an electrical engineering and computer vision perspective. His research is here.
Other related thoughts: The use of artists in war (and past wars).
Krawetz had a digital image analysis briefing a while back that was linked to on Wired. The link on wired appears dead but this PDF link appears to be the same briefing from memory. The briefing also covers the criminal side of digital imagery: child pornographers use methods of photographic manipulation to cover their, and their victims, trail and identities.
Books to Read
The Reconfigured Eye: Visual Truth in the Post-Photographic Era by William J. Mitchell
Photo Fakery: The History and Techniques of Photographic Deception and Manipulation by Dino A. Brugioni
Adobe Photoshop Forensics by Cynthia Baron (apparently the best forensics book out there, recommended by Krawetz)
The Commissar Vanishes: The Falsification of Photographs and Art in Stalin's Russia by David King (Examples of photos from book here)
Skin: The Complete Guide to Digitally Lighting, Photographing, and Retouching Faces and Bodies by Lee Varis
Digital Restoration From Start to Finish: How to repair old and damaged photographs by Ctein (I'm reminded of the great art forger Han van Meegeren. The guy used as much historically authentic material as possibly to create his forgeries e.g. actual paint and materials from the time. He was a schtickler for details. Could a photoshop forger do the same? I.e. someone 'finds' a box of old photos showing some old politician or influential person in some nefarious act or something. Could someone go the lengths of van Meegeren and recreate authentic old photos that passes at a technical level?)
Photoshop CS3 for Forensics Professionals: A Complete Digital Imaging Course for Investigators by George Reis (Not so much forensics on photos, but photoshop for use in forensics, might be some parallels or useful info?)
Lighting and the Dramatic Portrait: The Art of Celebrity and Editorial Photography by Michael Grecco
Propaganda, Rhetoric (I believe Sontag wrote something on photography as rhetoric ...), Art, Art Fraud