Without over thinking how meaning is conveyed through news photographs there seems to be a way of explaining the impact of an image more directly.
As in the construction of a sentence, photography, especially news photography, as its own grammatical issues. In a sentence is composed of a group of words that convey one central idea. Likewise news photographs must accomplish the same purpose. In a sentence there is a subject, a verb, and usually a direct object. What this means is that something or someone does something to somebody or something else. There is a central or dominant element acting upon another element.
This is essentially what news photography does -- it edifies. The meaning of an image is directly related to the arrangement of elements in the frame that attempts to convey one main idea, just as a subject in a sentence is relate to its predicate.
Ron Edmonds, a Pulitzer Prize winner, does this well with his photograph of the president gesturing at a news conference today. Without the gesture, the equivalent of a sentence's predicate -- all the elements besides the subject -- the picture would fail. In this case, the gesture helps to focus the viewer's attention on the intensity of the moment.
Without the gesturing moment, having only a tight shot of the president speaking at a podium would convey little more than saying that the photographer was there. Catching the president gesturing at just the right moment contributes meaning to the frame, just as a carefully worked predicate does in a sentence.