I recommended focusing on the tree photographs in my comments because it seemed like you were on a good track to discuss them in Writing Activity 1 and it seemed they might interest you enough to home in on your focused topic in photography (for example, why are they interesting, in what ways are they significant or important to the history of photography, what is interesting about the comparison between the positive and negative images you consider?). But you can choose any history of photography topic you like, so long as it deals with the history of photography.
The four short writing activities are not meant to be papers in and of themselves but are designed to help you work step-by-step towards writing your final paper on a topic in the history of photography that interests you. So I recommend that you do Writing Activities 2-4 on whatever topic you choose in photography (not Renaissance painting).
I hope that helps.