This paper proposes a new method for measuring vehicle geometric parameters, which is based on image processing. In the method, a black and white bar-cord ruler is applied to calculate the vehicle dimensions. Canny edge detection algorithm and image mosaic algorithm based on Image-Based Rendering (IBR) technique are utilized to deal with the target images. According to the relationship between the vehicle and the bar-cord ruler in the target images, the geometric parameters of the vehicle can be measured. Furthermore, the experiments indicate that the method has a good performance in measuring the dimensions of a vehicle.