This Union captain is captured in a double exposure photograph, or Photoshop 1860s style. The best brief explanation I’ve found is from an exhibit titled “Early Double Exposure Portraits” on lomography.com:
In the 1860’s photographers were looking for a way to boost their business. Because of this, they thought of a way to make the subjects appear twice in the photograph – thus the birth of double exposure. In the images presented here, you can see that the subject is seen twice in the photo but having a different position. To create this type of image, the photographer would shoot the subject in one position and then the subject must move swiftly to another position before the second image is taken. The photographers also used rotating lens caps and special plates to come up with these double-exposed images.