Now, allow me to post my own analysis of the picture as it intends to convey it's message. This is my own subjective interpretation, and is up for speculation of course.
When I first viewed the picture, I immediately had a sense of confusion. Everyone appears to be smiling, however they are situated in a pile of rubble, and the sign the young boy is holding says some nasty things on it.
This juxtaposition of positive and negative is symbolic of hypocrisy. But who is hypocritical here? Is it the boy, whose family has been destroyed, yet is still smiling? This would suggest the boy is betraying his own emotions. It also suggests that possibly the sign is a lie and nothing like that really happened to the boy. Or is the soldier hypocritical? If the sign is right, that he did do those awful things under a pretense to liberate and help the boy, then the soldier is certainly hypocritical.
Regardless of it all, it is quite obvious this photograph is staged - probably the soldier wrote the sign himself and had tricked the boy (who probably can't read English) into holding it and posing for a photograph, thinking the whole thing was quite hilarious. Or perhaps this photograph wasn't taken anywhere near Iraq, and everyone in the photo is some sort of actor? It's really irrelevant because the message of the photo is hypocrisy - that the very force who came to liberate lied, and really caused more harm than good.
So this is the message of the picture - whether or not you agree is up to you.