After the Challenger expedition (1872-1878), other nations started to show interest in oceanographic research and organizing their own expeditions. As of 1885, Prince Albert I of Monaco conducted oceanographic campaigns with the collaboration of some of the best marine biologists and physical oceanographers of the day, inventing new techniques and instruments for the oceanographic work. Prince Albert's scientific activity certainly helped kindle the interest of his friend, Dom Carlos I, king of Portugal, in the study of the oceans and marine life. Both shared the need to use photography to document their studies. This article analyzes the role of scientific photography in oceanography, especially in the expeditions organized by the Portuguese monarch.