A lot of mystery surrounds this photo. However, we know for sure it's a portrait of a Romanian oceanographer by Louis Boutan, taken sometime between 1893 and 1899 in Banyuls-sur-Mer, in the South of France. Louis Boutan was a French photography pioneer. At first he worked for a marine biology lab where he fell in love with diving. As time passed, Boutan wanted to show people the underwater world he had the privilege to experience.
With his brother's help, Louis invented his underwater camera in 1893. At the time it was considered to be advanced because the photographer/diver could adjust its diaphragm, plates, and shutter whilst underwater. However, the biggest challenge for Louis was lighting. With the flash photography rigs that were available it took Boutan about 30 minutes to correctly light his plates underwater.
His later invention involved a burning alcohol lamp on an oxygen-filled barrel. It used a rubber bulb to blow magnesium powder into the lamp, creating a flash. Even though this creation produced much better lighting than its peers, it was still very big. Boutan continued his work and made more and more compact portable flashes, smaller camera boxes and improved lenses. Louis Boutan was one of the few - if not the only - true underwater photographer of his time and pushed photography to new heights.
(h/t: petapixel, underwater360)