1. An image fusing method for fusing a thermal image and a visible image of a subject, the image fusing method comprising: determining importance of each pixel, based on a luminance value thereof, of the thermal image and the visible image; setting a pixel coefficient for each pixel of the thermal image based on the importance of each pixel of the thermal image and the visible image; generating another thermal image by applying the pixel coefficient to the luminance value of each pixel of the thermal image; and fusing the other thermal image and the visible image to generate a fused image, at an image fusing controller.