This paper describes how a culture, a technology, a design process, and a type of image coincided historically and depended on one another to produce their social effects. The conventions of screenshots – photographs of screens – were developed to describe the experience of using computer-aided design on an interactive computer. What was at stake was nothing less than what the word “computer” meant around 1960. While many architects at the time thought of computers as “mere tools,” protagonists of the Computer-Aided Design Project at MIT thought of computers as active partners and simulation environments. Describing screenshots as what Shapin (1984) calls a “literary technology of virtual witnessing” requires explaining how images are used in practice and taking what Latour (2014) derisively calls “iconographic conventions” seriously.