Thirty years ago, ISO/TC42 WG18, a newly created ISO working group on digital photography, began developing a standard to measure the spatial resolution of digital cameras. After years of proposals, testing, and analysis, consensus was reached on a test chart with tilted edge features for measuring spatial frequency response (SFR) and hyperbolic wedges for measuring visual and limiting resolution. The group ensured that the test chart and analysis software would be available internationally. First published in 2000, ISO 12233 is now used to measure cameras in a wide range of applications. It was revised in 2014 to define three new charts, a sine-wave modulated target in polar format, a low contrast e-SFR target, and the CIPA chart with software which computes a “human equivalent visual resolution” value. ISO 12233 is now being revised to provide improved results in challenging applications. This paper describes early resolution measurement approaches, and work in the 1990s to standardize the SFR method. It also describes enhancement made in later editions, including the 4th edition which is nearing publication.