From the New York Public Library's Digital Gallery, which has over 600,000 images from the NYPL's collections. I was searching around with keywords like gesture and posture, and found this: "Three soldiers carry a fourth to demonstrate one stage of the correct method to raise a soldier from a reclining position for carrying." It's clearly not so easy to hoist a comrade and then hold absolutely still for the many seconds necessary to make an 1860s photo.