From the BlackHat security conference in Las Vegas, a researcher and computer security consultant named Neal Krawetz presented a new tool for detecting manipulated photographs/videos:
Using a program he wrote (and provided on the conference CD-ROM) Krawetz could print out the quantization tables in a JPEG file (that indicate how the image was compressed) and determine the last tool that created the image -- that is, the make and model of the camera if the image is original or the version of Photoshop that was used to alter and re-save the image.
Comparing that data to the meta-data embedded in the image he could determine if the photo was original or had been re-saved or altered. Then, using error level analysis of an image he could determine what were the last parts of an image that were added or modified.
Krawetz used Al Qaeda videos as his examples, but it seems you might also get interesting results by running official government/oppo party photos through this program, or some of the stuff that appears on MSM websites.
There is a link to the source code in the original article.