Aerial reconnaissance, defined herein as the exploration of an area with air or space borne imaging systems for intelligence purposes, has a long and interesting history, and continues to thrive today. It has become a critical tool both in establishing military superiority and in keeping world peace. The reason aerial reconnaissance remains so important to the nations of the world is that the means by which it is performed and its information products continue to advance. The ever increasing capabilities of the imaging systems and usage of their products is driven by the extent to which their performance can be characterized and the product information communicated. This paper presents a historical review of the methods used for the evaluation of aerial reconnaissance system performance. The progression from long-used resolution methods, to today's use of imagery interpretability rating scales is described. Particular emphasis is paid to the CORONA years, a time in which much of the metric development work was accomplished.