The Gardner Gun
The British Library has dumped a massive trove of images into the Internet, and they don't have any copyright restrictions that I can see.
This one features an early form of the machine gun, which was used in the Sudan just long enough for the British to realize that sand could clog its mechanism and render it useless. The British lost, despite the presence of such a devastating weapon.
James Grant, of the 62nd regiment, is credited with the image. It comes from a book called Cassell's History of the War in the Soudan and was published in London in 1885.