The author doesn’t chronicle Cameron’s artistic development. We don’t get any discussion of her origin, her artistic influences, works she produced prior to The Passing of Arthur, etc.

This best captures the author’s purpose, which is to tell us that the combination of amateurism and artistry in Cameron’s work makes them interesting. The author indicates that the tension between Cameron’s aims (to portray scenes from fictional works) and the results she achieved (clearly amateurish, realistic pictures) gives her work a peculiar charm.

The author doesn’t focus on the “theatrical vision” of Cameron. In addition, the primary purpose isn’t about Cameron’s strengths and weaknesses. It’s just about certain features that make Cameron’s work interesting.

We’re never told that Cameron wanted to help photography gain prestige.

It’s not clear that there are any detractors of The Passing of Arthur. In any case, The Passing of Arthur is simply one example of Cameron’s work. The overall purpose doesn’t concern this specific example.