1. An image-shooting apparatus comprising: an image-shooting portion generating an input image by shooting; and a super-resolution processing portion performing super-resolution processing on a plurality of input images obtained from the image-shooting portion to generate an output image having a resolution equal to or higher than a resolution of the input images; wherein a shutter speed at which the image-shooting portion shoots at least one of the input images is made equal to or faster than a super-resolution limit shutter speed, which is a lower-limit shutter speed that enables the super-resolution processing to make the resolution of the output image equal to or higher than the resolution of the input images; further wherein there are a plurality of methods for the super-resolution processing performed by the super-resolution processing portion, and the super-resolution processing portion performs one of the plurality of methods selected based on an amount of exposure in the image-shooting portion, wherein the super-resolution processing portion includes; a high-resolution image generation portion fusing the plurality of input images together to generate a high-resolution image; an averaging processing portion that applies averaging processing to the plurality of input images to generate an averaged image; and a weighted addition processing portion performing weighted addition processing on the high-resolution image and a predetermined image to generate a weighted added image, and when the amount of exposure is less than a first threshold value, the weighted addition processing portion generates the weighted added image by performing weighted addition processing on the high-resolution image and an image based on the averaged image, and the weighted added image is taken as the output image.