Well, I did a search and can’t find it. Oddly, another person asked “Answer.com” the same question, noting he had seen this painting, and there was no real answer. So I know it exists. But it apparently is not Troiani or Kunstler, two of the more famous Civil War artists.
An image of the painting is here:
http://jessicajewettonline.blogspot.com/2011/04/what-does-civil-war-mean-to-me.html
It’s the only one I found when I googled it, and the site doesn’t give any details.
Here you go:
http://www.lloydgarrison.com/wargallery.htm
There are two of J. Chamberlain and ghosts.