Many of the original Civil War photographs on the Library of Congress site have flaws (such as a cracked glass plate, parts of the negative missing) that accumulated over the years before they were rephotographed. Although these "flaws" do help us to recognize that the photos were taken long ago, I personally like to see them as they were when they were recently taken. Thus, a number of the original photos have been digitally restored--not to add any details, but to present them very much as they appeared to the first viewers.
Below is an example of a photograph before and after a digital restoration:
