I 've seen three different types of artists being credited as doing photography.
Firstly is the performance artist who does the actions of camera use: basically pointing, looking, clicking. Eventually the camera won't click anymore because some gizmo inside it is full or used up. Hand the gizmo (CF card, casette, spool with funny paper on it, whatever ?) to a helpful person along with some money and eventually pictures come back. The performance artist is (somehow) a photographer. Ironically the performance artist does not need to know that the photographic medium exists. Just do the actions, pay the money, and pictures follow. A contentious example would be Henri Cartier-Bresson. Only by the thinnest coincidence of history and technology did he do his camera work when film was the ordinary stuff to put in cameras. In other eras his pictures would still be wonderful but not photographs. H. C-B, I suspect, would not care a damn.
There are those who know the medium, nuance the light, do the processing and end up with pictures consisting of accumulated marks occasioned by the impact of light. Since the products of their work are indubitably photographs I guess these folks are photographers too. Examples would include E. Weston, A.Adams and most APUGers.
In recent years a new species of artist has evolved whose medium is photographs. No, not making photographs but rather making art out of photographs. End products of their work are often collages, assemblages, installations. Arthur C. Danto, the American writer, has suggested the word photographist instead of photographer for these workers. I would suggest some major art from David Hockney or Bill Henson would fall firmly into the photographist category.