A method includes setting an exposure time of an image sensor included in a terminal device so that, in an image obtained by capturing a subject by the image sensor, a bright line corresponding to each of a plurality of exposure lines included in the image sensor appears according to a change in luminance of the subject. The method also includes obtaining a bright line image including a plurality of bright lines, by capturing the subject that changes in luminance by the image sensor with the set exposure time. The method further includes estimating a plurality of center areas each of which is in each of the plurality of bright lines, and obtaining identification information of the subject, by demodulating data specified by a pattern of the plurality of center areas.