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; 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: 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 determining a ratio of the summed values respectively computed for the first and second sets of pixels, wherein the program instructions for determining the ratio of the summed values comprise program instructions for dividing the summed values computed for the second set of pixels by the summed values computed for the first set of pixels, and wherein the program instructions for accepting or rejecting the plurality of pixels comprise program instructions for: accepting the plurality of pixels for further evaluation upon determining the ratio differs from a set value by an amount less than or equal to a second predetermined threshold distinct from the first predetermined threshold; and rejecting the plurality of pixels for further evaluation upon determining the ratio differs from the set value by an amount greater than the second predetermined threshold.