A distinguishing method of distinguishing an imaging object by an imaging device comprising an imager and an illuminator configured to illuminate the imaging object of the imager, the method comprising: performing respective imagings according to plural imaging conditions each including an exposure time (te) of the imager and an amount of illumination to the imaging object by the illuminator, the respective imaging conditions being different from one another; calculating respective brightnesses of respective images obtained by the respective imagings from data of the obtained images; storing respective combinations of the calculated brightnesses of the respective images obtained by the respective imagings and the imaging conditions of the respective images in a memory; and calculating an estimate of a first parameter ( k_ off) indicating degree of influence of variation of the exposure time (te) on the brightness of images and/or an estimate of a second parameter ( k_on) indicating degree of influence of variation of the amount of the illumination on the brightness of images, based on plural combinations of the stored combinations of the brightnesses and the imaging conditions stored in the memory; and determining that the imaging object of the imager is a light-emitting body when a predetermined condition is satisfied, the predetermined condition being any one of: the estimate of the first parameter ( k_ off) is larger than a first threshold; the estimate of the second parameter (k on) is smaller than a second threshold; the estimate of the first parameter ( k_ off) is larger than the first threshold and the estimate of the second parameter ( k_on) is smaller than the second threshold; and a ratio of the estimate of the first parameter (k_off) to the estimate of the second parameter (k on) is larger than a third threshold. performing respective imagings according to plural imaging conditions each including an exposure time (te) of the imager and an amount of illumination to the imaging object by the illuminator, the respective imaging conditions being different from one another; calculating respective brightnesses of respective images obtained by the respective imagings from data of the obtained images; storing respective combinations of the calculated brightnesses of the respective images obtained by the respective imagings and the imaging conditions of the respective images in a memory; and calculating an estimate of a first parameter ( k_ off) indicating degree of influence of variation of the exposure time (te) on the brightness of images and/or an estimate of a second parameter ( k_on) indicating degree of influence of variation of the amount of the illumination on the brightness of images, based on plural combinations of the stored combinations of the brightnesses and the imaging conditions stored in the memory; and determining that the imaging object of the imager is a light-emitting body when a predetermined condition is satisfied, the predetermined condition being any one of: the estimate of the first parameter ( k_ off) is larger than a first threshold; the estimate of the second parameter (k on) is smaller than a second threshold; the estimate of the first parameter ( k_ off) is larger than the first threshold and the estimate of the second parameter ( k_on) is smaller than the second threshold; and a ratio of the estimate of the first parameter (k_off) to the estimate of the second parameter (k on) is larger than a third threshold. the estimate of the first parameter ( k_ off) is larger than a first threshold; the estimate of the second parameter (k on) is smaller than a second threshold; the estimate of the first parameter ( k_ off) is larger than the first threshold and the estimate of the second parameter ( k_on) is smaller than the second threshold; and a ratio of the estimate of the first parameter (k_off) to the estimate of the second parameter (k on) is larger than a third threshold.