It's important to remember that photographs don't necessarily have to be modified to be propaganda. Consider this one, sent out by the Associated Press from their coverage of the London protests.
Notice how the photograph was taken from a low angle? The photographer clearly intended to present a "David vs. Goliath" scenario, with the United States predictably being shoe-horned into Goliath's role. (It's comforting to see that ANSWER has already modified their protest to be against the "US/Israeli war.") Who fills the shoes of the righteous David? Why, of course—Hezbullah does!
I have a feeling we'll be seeing more of this photo, as it's much more "emotion-filled" than the one taken moments before.
I look forward to continuing with my hunt for photographic propaganda.