This image of Texas Jack (right, mounted) at Fort McPherson, Nebraska, was recently digitized by the Lincoln County Historical Museum in North Platte, Nebraska. It shows Jack with his friends and hunting companions the Earl of Dunraven and Dr. George Kingsley.
Information about the photograph, and the museum, can be seen at: https://www.dimelibrary.com/post/texas-jack-at-fort-mcpherson