Abstract: The present invention is concerned with an automatic recognition of image data representative of crack derived from measurements of the road surface using a computor (4). An image memory in which data on the road surface are stored is divided into a plurality of regions and the region constituting a part of the divided regions for which a determination has been made such that crack (LP) is existent is utilized as a start point for a pursuing operation. A series of processings of pursuit and extraction such as extracting line segments (SG) corresponding to the crack (LP) from the start point region, making a determination on the direction of pursuing to be next effected on the basis of the line direction (.theta.