But as to their impact, I would guess that the images themselves don't necessarily turn people against any given war.

The graphic images of Vietnam, from the images of our soldiers, to photographs of things like My Lai, were a major part of the conversation.  But they didn't "turn" people against the war.  The change in public mood only occured once the "credibility" gap started to emerge after 1968 (the gap between what he administration had been telling us -- "relax, we are winning the war" -- and the story on the ground).   But here again, it wasn't the "press" that turned the public against Vietnam -- it was a combination of hubris, failed policy, and the government's lies.