1. A method for detecting cracks from an object image, the method comprising the steps of: dividing a region of the object image into a plurality of pixels; inverting a grayscale value of each of the plurality of pixels; preparing a group of filters with different rotational orientation components and applying one of the filters to the plurality of pixels; setting values of pixels with filter responses greater than or equal to a first threshold value to 1 and setting values of the other pixels to 0; applying a filter, to the plurality of pixels, wherein the filter responds to spatial frequencies of edges of white lines; replacing a set value of a pixel with 0 if an absolute value of a filter response corresponding to the pixel is greater than or equal to a second threshold value and the set value of the pixel is 1; and extracting a line segment vector estimated to correspond to a crack by using a transform that estimates continuity of the plurality of pixels.