1. A non-transitory storage medium having program instructions which are executable by a processor for: analyzing an image of particles having fluorescence-material associated therewith to identify one or more pixels within the image that exhibit an optical parameter value above a first predetermined threshold; determining locations within sets of the one or more identified pixels that respectively exhibit maximum values for the optical parameter within the sets; subsequently computing a rate of intensity change of the optical parameter for a plurality of pixels surrounding at least one of the locations to determine whether the plurality of pixels is indicative of a single particle within the image of particles or a clump of particles within the image of particles; and accepting or rejecting the plurality of pixels for further evaluation based upon the computed rate of intensity change.