Photoshopping as crude as the one here is rare. In fact, photoshopping at all is probably rare. Much more common are cases where the photo is real, but the events and context represented are not what actually happened, or may even be staged. One infamous case from not too long ago was after a CIA predator strike on Al Qaeda in Pakistan. There was a photo alleging to be remains of the rocket, perched on a crumbling wall, with villagers posing behind it. The obvious problem with the photo, though, was that the supposed rocket remains were not rocket remains at all, but rather an unexploded artillery shell. The difference is clear and unambiguous to anyone with even a little bit of military knowledge, though it takes a bit more digging to figure out that the shell was most likely Pakistani. But even basic military knowledge seems woefully missing from the press, and so they screw things up time and time again. And it makes them particularly susceptible to influence from the side that lies the most, which in this case is Hezballah.
In the current conflict, there have also been reports of an Israeli attack on an ambulance, complete with photos of where a missile supposedly struck the ambulance, right in the middle of the red cross on its roof:
http://www.commondreams.org/headlines06/0725-05.htm
Damning photo, isn't it? But there's a small problem: Megan, the author of the article, has been played for a fool. Whatever the hell hit that ambulance, it was most assuredly NOT an Israeli missile. If it were, nobody from that ambulance would be alive, and the ambulance itself would probably be several large chunks of twisted, barely recognizable metal, rather than just a van with a small hole in the roof.
You can see a few more photos here.
http://images.search.yahoo.com/search/images?ei=UTF-8&p=lebanon tyre ambulance&fr2=tab-news
Note that where the paint on the rooftop of the ambulance has been blasted away, the underlying metal appears rusted. To my eye, this suggests that the damage was not even recently sustained. The photos are probably all be real, but that doesn't mean that any of them depict what the captions claim.