A method of correcting an image by an image correcting apparatus, the method comprising: an acquiring step of acquiring, by an acquiring section of the image correcting apparatus, a plurality of images each including in at least a portion thereof a surface of a metal strip in a steady state, the metal strip being rolled by a rolling mill, the images being captured under different illuminating conditions or image capturing conditions by a camera (61, 62, 63, 64, 65) disposed in a predetermined position; a selecting step of selecting, by a selecting section of the image correcting apparatus, a reference pixel point or a reference pixel range from an image portion of each of the images that includes the metal strip reflecting light area where reflected light is stronger than in other areas in the portion including the metal strip, from the images acquired in the acquiring step; a determining step of determining, by a determining section of the image correcting apparatus, as a first image, an image including the reference pixel point or the reference pixel range where a luminance of any one of an R value, a G value, and a B value in average in the reference pixel point or the reference pixel range is highest, from among the images acquired in the acquiring step; a calculating step of calculating, by a calculating section of the image correcting apparatus, luminance differences between (i) the R value, the G value, and the B value in the reference pixel point or the R value, the G value, and the B value in average in the reference pixel range in the first image and (ii) an R value, a G value, and a B value in a reference pixel point or an R value, a G value, and a B value in average in a reference pixel range in the same area as the reference pixel point or the reference pixel range in the first image, respectively, for all the images other than the first image; and a correcting step of adding or subtracting, by a correcting section of the image correcting apparatus, an absolute value of each of the luminance differences to or from a corresponding one of the R value, the G value, and the B value at all pixel points of all the other images so as to cause the R value, the G value, and the B value in the reference pixel point or the R value, the G value, and the B value in average in the reference pixel range of all the other images to match the R value, the G value, and the B value in the reference pixel point or the R value, the G value, and the B value in average in the reference pixel range of the first image. an acquiring step of acquiring, by an acquiring section of the image correcting apparatus, a plurality of images each including in at least a portion thereof a surface of a metal strip in a steady state, the metal strip being rolled by a rolling mill, the images being captured under different illuminating conditions or image capturing conditions by a camera (61, 62, 63, 64, 65) disposed in a predetermined position; a selecting step of selecting, by a selecting section of the image correcting apparatus, a reference pixel point or a reference pixel range from an image portion of each of the images that includes the metal strip reflecting light area where reflected light is stronger than in other areas in the portion including the metal strip, from the images acquired in the acquiring step; a determining step of determining, by a determining section of the image correcting apparatus, as a first image, an image including the reference pixel point or the reference pixel range where a luminance of any one of an R value, a G value, and a B value in average in the reference pixel point or the reference pixel range is highest, from among the images acquired in the acquiring step; a calculating step of calculating, by a calculating section of the image correcting apparatus, luminance differences between (i) the R value, the G value, and the B value in the reference pixel point or the R value, the G value, and the B value in average in the reference pixel range in the first image and (ii) an R value, a G value, and a B value in a reference pixel point or an R value, a G value, and a B value in average in a reference pixel range in the same area as the reference pixel point or the reference pixel range in the first image, respectively, for all the images other than the first image; and a correcting step of adding or subtracting, by a correcting section of the image correcting apparatus, an absolute value of each of the luminance differences to or from a corresponding one of the R value, the G value, and the B value at all pixel points of all the other images so as to cause the R value, the G value, and the B value in the reference pixel point or the R value, the G value, and the B value in average in the reference pixel range of all the other images to match the R value, the G value, and the B value in the reference pixel point or the R value, the G value, and the B value in average in the reference pixel range of the first image.