In this paper,we propose an approach in which pixels on fingerprint ridges can be traced.Based on the proposed approach,an algorithm to remove pseudo structures from a thinned fingerprint image was developed.The algorithm is carried into execution using a library of thinned fingerprint images with such pseudo structures as spurs,bridges and holes.It is found that these pseudo structures can be accurately and totally removed,and on the other hand,the processing speed is high,compared with the conventional algorithms which often turn out to be of less efficiency and effect.