The development of road transportation makes it easier for people to drive their vehicles. Unfortunately, it also causes the increasing number of traffic accidents. Advanced driver assistance systems, which in many ways is based on the future trajectory prediction of the vehicle, are developed to alert the driver for potential dangers. Road conditions, including road geometry and the distance between lead vehicle and host vehicle, are important factors in improving accuracy of future trajectory prediction. The road conditions can be obtained by the camera affixed in the vehicle. In this paper, we propose an image processing system, which includes a curve detection algorithm (CDA) and a distance conversion (DC) algorithm, to obtain these road conditions from the image. First, CDA detects the lane stripes and calculates the vanishing point. The road trend can then be identified according to the location of the vanishing point. DC is used to convert the distance between the lead and host vehicles in the image to the real distance. Through analyses and experiments, it is shown that the proposed system achieves a higher precision than the baseline algorithms.