1. An information-processing device having the following functions: performing free-space optical communication to receive predetermined pieces of information from a remote transmitter device having a light source that emits light containing at least the aforementioned pieces of information; capturing an image of a certain imaging range; and obtaining position information of the light emitted from the light source of the transmitter device present. within the imaging range in parallel to capturing plural frames of images of the same imaging range, and the information-processing device includes: a) an imaging device including a photo-receiver having a two-dimensional array of normal pixel cells, each of which performs photoelectric conversion, and a readout circuit for reading out a pixel signal produced by the photoelectric conversion at each pixel cell; b) a binning processor for creating a set of binned images having different resolutions from each frame of the image, where each binned image is created using signals of expanded pixel cells, each of which is created by virtually adding pixel signals of adjacent pixel cells selected from all the normal pixel cells of the imaging device; c) an evaluator for processing the signal of a given normal or expanded pixel cell to determine whether the pixel cell is receiving the light emitted from the light source, by analyzing a predetermined number of frames of images that are temporally adjacent to or in proximity to each other and calculating an evaluation index that reflects a presence of the emitted light; and d) a pixel cell locator for performing a process including the following steps: (d1) locating one or more expanded pixel cells that are receiving the light emitted from the light source within the binned image having the lowest resolution created by the binning processor, based on the evaluation indexes that the evaluator has given to the expanded pixel cells of the binned image concerned; (d2) defining a limited range within the binned image having the next lowest resolution, including the one or more expanded pixel cells located in the previous step; (d3) locating one or more expanded or normal pixel cells that are receiving the light emitted from the light source within the aforementioned limited range of the binned image, based on the evaluation indexes that the evaluator has given to the expanded or normal pixel cells included in the aforementioned limited range; and (d4) returning to step (d2) until one or more normal pixel cells that are receiving the light emitted from the light source are located in step (d3).