A computer-implemented method of performing image processing for images of biological objects includes: storing definitions of a plurality of descriptors; receiving image data relating to an image of a reference population of biological objects; receiving image data relating to an image of a target population of biological objects; processing the reference population image data to obtain a reference set of measurements, containing data for each of the descriptors; processing the target population image data to obtain a target set of measurements, containing data for each of the descriptors; and selecting a combination of the descriptors on the basis of comparing the reference set with the target set to define a preferred combination of the descriptors for use in identifying characteristics of a further population of biological objects which are similar to those of the target population.