What is a formal analysis? A formal analysis is basically a breaking down of an artworks parts in order to understand its whole. This means, there is a detailed look at how the artwork uses the elements and principles of design.
Elements of Design: Color, Form, Line, Mass, Shape, Space, Texture, Time and Motion, Value and Volume
Principles of Design: Balance, Contrast, Emphasis, Focal Point, Pattern, Proportion, Rhythm, Scale, Unity, Variety
Photography has some elements that are used more than in other arts like contrast and tonal range in the case of a black and white photograph. Specific to photography are depth of field meaning how much of the photograph is in focus and exposure time. The exposure time determines whether moving subjects are stopped or in motion.
Photography is unique because if you are viewing a reproduction in a book, you are typically only seeing the image and not the paper the image is printed on. It is important to note that while a photograph may be considered a two-dimensional object, if printed they are an object with a sliver of dimension. If you are lucky enough to be analyzing a photographic object (the print itself), you can also discuss the size of the paper, is it framed, if not is there anything written or stuck on the back of the photograph, does the paper show wear, has the image faded, has the photograph been torn from an old photo album, has the photograph been written on or defaced in any way and so forth?
Keep in mind that an analysis goes beyond just a description. An analysis is proving a point. What do all of the elements you have discussed say about the art object.