Method for inspection of flat objects (10, 12, 14, 16, 18, 20, 24, 26, 28, 30) comprising the steps of: (a) taking a digital image of the object surface of several objects (10, 12, 14, 16, 18, 20, 24, 26, 28, 30) of the same kind of a series, wherein each digital image consists of a plurality of image points with an intensity value relating to each image point; and (b) detecting defects (32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52) on the respective object surface by comparing the taken image with a reference image; (c) wherein the images of the objects (10, 12, 14, 16, 18, 20, 24, 26, 28, 30) of the entire series are taken before the comparison with the reference image, and (d) the reference image is generated from several or all images of the series; wherein (i) the image points of the images used for generating the reference image are mathematically separated into several image portions (58, 60) and the intensity value of the image points are at first allocated to the portions, from which it is derived; (ii) a moving average of the intensity values of the image portions is calculated by adding up the intensity values for each point of the image portion of the image portions within the area of an original image point and allocated to the central point of the image portion; (iii) the images generated with the moving average are superimposed and shifted against each other by a value where a minimum difference of the corresponding intensity values of the image portions is achieved and (iv) the reference image is generated with such image which is shifted by this value. (a) taking a digital image of the object surface of several objects (10, 12, 14, 16, 18, 20, 24, 26, 28, 30) of the same kind of a series, wherein each digital image consists of a plurality of image points with an intensity value relating to each image point; and (b) detecting defects (32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52) on the respective object surface by comparing the taken image with a reference image; (c) wherein the images of the objects (10, 12, 14, 16, 18, 20, 24, 26, 28, 30) of the entire series are taken before the comparison with the reference image, and (d) the reference image is generated from several or all images of the series; wherein (i) the image points of the images used for generating the reference image are mathematically separated into several image portions (58, 60) and the intensity value of the image points are at first allocated to the portions, from which it is derived; (ii) a moving average of the intensity values of the image portions is calculated by adding up the intensity values for each point of the image portion of the image portions within the area of an original image point and allocated to the central point of the image portion; (iii) the images generated with the moving average are superimposed and shifted against each other by a value where a minimum difference of the corresponding intensity values of the image portions is achieved and (iv) the reference image is generated with such image which is shifted by this value. (i) the image points of the images used for generating the reference image are mathematically separated into several image portions (58, 60) and the intensity value of the image points are at first allocated to the portions, from which it is derived; (ii) a moving average of the intensity values of the image portions is calculated by adding up the intensity values for each point of the image portion of the image portions within the area of an original image point and allocated to the central point of the image portion; (iii) the images generated with the moving average are superimposed and shifted against each other by a value where a minimum difference of the corresponding intensity values of the image portions is achieved and (iv) the reference image is generated with such image which is shifted by this value.