The single image which says it all - the holy grail of photojournalism - is the epitome of clarity. With nothing left to say, the image is "complete" (Roland Barthes) and the viewer plays no role in the interpretation. Thematically clear images run the danger of being passed over quickly precisely because of their communicative efficiency due to a lack of involvement; of the lack of a need on the viewer's part, to invest in its understanding (the converse of ambiguous images).
This makes it all the more important for the clear image to be compelling. If the image is captivating and powerful to the creator, it will be so to the viewer as well.