One of the first things you might consider when looking for primary sources for your research is what kinds of things are common to the time. What types of communication, documentation and material culture were produced in the mid-nineteenth century and by the people/events you are interested in? A little background knowledge and a little imagination can start you off on the path by using specific search systems and keywords.
Common Search Terms & Keywords
Books are an excellent place to find reprints and transcriptions of original documents and images. You can use Keywords to search for books, or the Subject Heading for primary sources "Sources" by changing the drop down from "Any Field" to "Subjects."
The mid-1800s were a time of great change for communication in the United States. The advacnes in transportation and the telegraph dramatically increased the speed information traveled. Furthermore, the federal government subsidized the distribution of newspapers through the U.S. Postal System. Communication with the public was vital to the war effort on both sides, and modern journalism as the profession we think of today was formed as a part of that. However, newspapers were still quite different than today and were often heavily partisan (backed by a political party or group).
Understanding how newspapers functioned during and after the Civil War is vital to place them (and the information they give) in the context of the times. See the following for brief overviews.
While early photographic processes such as the Daguerreotype existed during the Civil War, it was not until the late 1800s that photographs were printed in newspapers, and not until the early 1900s that it became a regular practice. However, with the invention of the Lithograph, illustrations were common in the news. Political Cartoons were also a common way of influencing readers.