1. An image-based measurement system for measuring subjects in a dynamic state or in use, the image-based measuring system comprising: an active imaging means for providing an active image by actively imaging a subject of measurement, wherein the subject of measurement is actively imaged while in a dynamic state or in use, a reference image means that provides a reference image of the subject of measurement, the reference image being of an image type different from the active image, an image combining means that combines the reference image and the active image, matched in scale and keyed together, and an image measurement means that measures the active image relative to the reference image, and provides measurements of dimensions of components and/or spacings between components of the subject of measurement, when the subject of measurement is in a dynamic state or in use.