To write a comparison is to look at the similarities and differences in two artworks or photographs. This can lead to new discoveries about both works. This type of writing like the others requires a thesis statement or idea that you are arguing about the two works.
It is important to note that the photographs you choose to compare should relate in some way (culture, time period, medium, genre, ect). For example, I asked a group of students to compare two landscape photographs, one by 19th century American photographer Timothy O’Sullivan and 21st century British/Indian photographer Max Kandhola to understand the different meanings behind these two works. This is one example comparisons I wrote.
There are two ways you can go about writing comparisons. You can write about one photograph and then the other or you can alternate between the two using alternating paragraphs or sentences. I would suggest perhaps a combination of the two. It seems logical to alternate talking about the similarities of the photograph in the same paragraph or paragraphs, while perhaps you separate the differences of the works in their own paragraphs.