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; wherein the program instructions for computing the rate of intensity change comprise program instructions for: subtracting a background signal from the image; summing values of the optical parameter for a first set of the plurality of pixels arranged within a first predetermined radius surrounding the at least one location; summing values of the optical parameter for a second set of the plurality of pixels arranged within a second predetermined radius surrounding the at least one location, wherein the second predetermined radius is larger than the first predetermined radius; and accepting the plurality of pixels for further evaluation if the summed value for the first set of the plurality of pixels is approximately equal to the summed value for the second set of the plurality of pixels.