2. It tells the reader which photographs are being discussed.
4.It creates a compound-complex sentence.
A compound-complex sentence brings both a compound sentence and a complex sentence forms together. In other words, it contains at least two independent clauses (like a compound sentence) and at least one dependent clause (like a complex sentence).
Moreover, the underlined clause is modifying the main noun of the sentence, so that it is adding information about the photographs.
D that is because it is the information about a period, the place, and the event taht created, influenced, and formed the background to historical records