1. A method comprising: acquiring a two-dimensional image of a plurality of particles, wherein the plurality of particles includes a plurality of calibration particles having Gaussian intensity profiles based on internal distributions of a first fluorescent material, and a plurality of non-calibration particles having non-Gaussian intensity profiles based on surface distributions of a second fluorescent material; identifying a calibration particle of the plurality of calibration particles by correlating a portion of the image corresponding to the calibration particle to a Gaussian function; measuring an intensity of the calibration particle; and normalizing an intensity of the image based at least in part on the intensity of the calibration particle.