As computer vision systems are increasingly developed and tested in the real-world, there is a significant need to formalize the process of system design and analysis so that engineers can rapidly design, test, and deploy vision systems for real-world applications. Our objective in this paper is to analyze the system design, analysis, and refinement cycle through a case study involving the systematic engineering of a dual-camera video surveillance system for people detection and zooming. We illustrate how an existing system designed and analyzed by following rigorous systematic engineering principles can be extended to relax the system operating conditions with minimal re-design and analysis efforts. The key conclusion is that by choosing appropriate modules and suitable statistical representations, we are able to re-use existing system design and performance analysis results.