1. An image recognition device, comprising: an image sensor that captures an image via an image forming optical system and outputs image information repeatedly; a detector that detects differences between reference image information related to a reference image and a plurality of sets of partial information included in the image information; a recognition circuit that includes a microprocessor and recognizes a set of partial information, for which a smallest difference value among a plurality of differences detected in correspondence to the plurality of sets of partial information is calculated, as information matching the reference image information if the smallest value is smaller than a threshold value; and a controller that includes a microprocessor and sets the threshold value in correspondence to a color indicated in the reference image information.