Pavement crack is the main form of early diseases of pavement. The use of digital photography to record pavement images and subsequent crack detection and classification has undergone continuous improvements over the past decade. Digital image processing has been applied to detect the pavement crack for its advantages of large amount of information and automatic detection. The applications of digital image processing in pavement crack detection, distresses classification and evaluation were reviewed in the paper. The key problems were analyzed, such as image enhancement, image segmentation and edge detection. The experiment results of the commonly used algorithms forcefully supported following conclusion: the noise in pavement crack images is effectively removed by median filtering, the histogram modification technique is a useable segmentation approach, the canny edge detection is an ideal identification approach of pavement distresses.