A close-up of this photo reveals that the woman seated is wearing a brooch with a man's photograph on it, but for some reason it's sideways!
The orange 2-cent tax stamp on the back of the photo indicates that it was taken between 1864 and 1866. These tax stamps were affixed to various goods during these years as the result of an act passed by the federal government to help pay for the Civil War. Wilkinson would have attached the stamp, then cancelled it by adding his initials and the date. Although this was a very unpopular tax at the time, we can be grateful for it now - it is a great aid in dating photographs! The stamp on this photo appears to have the year 1865 written on it.
Another photo provided by Brenna, also taken by Wilkinson, does not have a tax stamp. Based on the woman's large hoop skirt, I would guess that it was taken prior to 1864.
Harrell-Sesniak, "Dating Old Family Photographs with Civil War Revenue Stamps," Genealogybank.com blog. Posted 14 November 14 2012. http://blog.genealogybank.com/dating-old-family-photographs-with-civil-war-revenue-stamps.html