Low-cost license plate detection using a calibrated camera

This paper presents a new approach for automatic license plate detection using an embedded camera inside a moving vehicle, implemented in a low-cost prototype. The key idea of the proposed method is to initially identify shadowed regions under the rear of visible vehicles, and then explore information from a calibrated camera to reduce the search space for license plates. Within the search space, any “baseline” detector can be used, and the results are validated exploring the expected size of a license plate in world coordinates and the known camera parameters. Our experimental results show that we can increase the speed of a “baseline” detector by 93%, and at the same time improving the f-score (increase in precision without significant loss in recall).