1. An image transmission system comprising: a transmission device comprising: one or more first processors, and at least one first memory coupled to the one or more first processors, the at least one first memory having instructions stored thereon which, when executed by the one or more first processors, cause the transmission device to: divide image data into a plurality of regions on the basis of a similarity of pixels, and transmit the image data and region representative points of the plurality of regions; and a reception device comprising: one or more second processors, and at least one second memory coupled to the one or more second processors, the at least one second memory having instructions stored thereon which, when executed by the one or more second processors, cause the reception device to: receive the image data and the region representative points transmitted from the transmission device, assign, for each pixel in the image data, one of the region representative points based on distances between respective region representative points and the pixel in a feature space, update a location and a pixel value of the region representative point in the image data on the basis of locations and pixel values of pixels assigned to the region representative point, and generate region labels used for identifying the plurality of regions, using the image data and the region representative points whose location and pixel value have been updated.