1. A computer-implemented method of performing image processing for images of biological objects, said method comprising: a) storing definitions of each of a plurality of descriptors for which measurements can be taken in relation to said biological objects; b) receiving image data relating to an image of a reference population of biological objects exposed to a given biological environment; c) receiving image data relating to an image of a target population of biological objects exposed to a different given biological environment; d) processing said reference population image data to obtain a reference set of measurements, containing data for each of said plurality of descriptors; e) processing said target population image data to obtain a target set of measurements, containing data for each of said plurality of descriptors; and f) selecting a combination of one or more of said plurality of descriptors on the basis of comparing said reference measurement data with said target measurements data to define a preferred combination of said descriptors for use in identifying characteristics of a further population of biological objects which are similar to those of the target population.