1. A method of analyzing a plurality of biological entities using an imaging apparatus, the method comprising: a) acquiring a first image of the biological entities; b) adding a marker to said plurality of biological entities after the first image is acquired, said marker being capable of identifying objects within said plurality of biological entities when detected using the imaging apparatus, c) recording a marked-up image in which spatial definitions of said objects are identifiable from said marker; and d) generating a spatial definition for an object in said first image using data derived from said marked-up image; e) acquiring an initial series of images before adding a marker and recording a marked up image, and applying the spatial definition to the initial series of images to enable an operator to evaluate changes in the object over time.