Intelligent Transportation System (ITS) provides various services for vehicular environments. Many of them require accuracy information about vehicle's position. However, the current positioning techniques may not satisfy the accuracy requirement, especially for safety applications. In this paper, we propose a Video-Assisted Inter-Vehicle Positioning (VIP) system. The system integrates processed image data from video sensors equipped on part of vehicles and inter-vehicle communication techniques. The system equips each vehicle with a GPS and inter-vehicle communication modules, and a part of vehicles are equipped with a video sensor. The data extracted from video sensors will be exchanged among vehicles and assist each vehicle to validate the position received from neighboring vehicles so as to improve the accuracy of cooperative positioning. Simulation results shown that our approach can achieve 30 percent of improvement in the position accuracy when only half of vehicles were fully equipped, and improve the accuracy by factor of 40 percent (within 3m) if all vehicles were fully equipped.