An image process for determining whether an image is foggy determines a shape of a road for driving of a vehicle in an image captured by an onboard camera based on white road line recognition. Based on the road shape, the process determines, in the image, a distant road area on the road for driving at a specified distance from the vehicle. The process processes, of the entire image captured by the camera, an image portion corresponding to the distant road area to determine whether an image is foggy. Thus, a load on image processing decreases compared with analysis of the entire image. The distant road area is located on the road at the specified distance far from the vehicle in the image. Generally, a road continues in the distance. Since the corresponding area possibly captures a distant part, the fog determination accuracy can be ensured.