Photographs are not simply images but also historically shaped three-dimensional objects. They hold a physical presence, bear traces of handling and use, and circulate in social, political and institutional networks. Beyond their visual content, they are increasingly acknowledged as material “actors,” not only indexically representing the objects they depict, but also playing a crucial role in the processes of knowledge-making within scientific practices. This has a historical dimension: most scientific disciplines rapidly adopted photography as an important research tool. Thereby, the various material qualities of photographs afforded certain types of uses in those disciplines. Specialized photo archives were founded as interfaces of technology and science and as laboratories for scientific thought.