Photographs have helped us learn about our world's history over the past 100 years. Photographers carrying around massive equipment in the late 1800 s captured scenes from their time which now enable us as viewers to develop a mental picture of something that we would otherwise have no way of knowing about.
Photographs are tools for learning.
Through their images, they describe how something might have looked. They process factual information by exposing details of a person or place at a particular time. For those who weren't present at a certain place at a certain time, photographs have preserved that situation for them so they are able to have an idea of what actually did occur. Photographs provide a more personal, up-close perspective on things, than most words can do. Some situations are difficult to explain in words, and unless you were there, you have no way of understanding what that situation was like.