High-speed, in situ video microscopy is a promising technology for measuring critical solid-phase properties in suspension crystallization processes. This paper demonstrates the feasibility of high-resolution, video-imaging-based particle size distribution (PSD) measurement by applying image analysis and statistical estimation tools to images from a simulated batch crystallization of an industrial photochemical. The results also demonstrate the ability to monitor important quality parameters, such as the ratio of nuclei mass to seed mass, that cannot be monitored by conventional technologies. General recommendations are given for achieving appropriate sampling conditions to enable effective imaging-based PSD measurement. (C) 2009 American Institute of Chemical Engineers AIChE J, 55: 896-905, 2009