车牌识别问题是当前国内研究的一个热点方向，它的研究成功对车牌控制、运输安排等有着重要的应用价值。为了解决在车牌识别中的首要问题--车牌的自动定位技术，根据车牌目标在图象中的成像特点，提出了基于投影不变性的车牌自动检测定位方法，在车牌歪斜角度不大的情况下，成功地从复杂背景中检测定位出了车牌，通过现场实际测试，该方法取得了较好的定位识别效果。

The issue of car license plate recognition is a focus direction of studying both at home and abroad at present, its success has important application values in vehicle controlling, transportation management, parking and so-so. There are many papers published in the research domain. In order to solve the primary problem of the car license plate recognition--Automatic orientation technology of the car license plates, a method of automatic detection and orientation of car license plate based on license plate's projection invariability in the condition of lesser deflection of car license is presented in terms of the imaging characteristics of the car license plate target, which can succeed in detecting and orienting the car license plate from the complicated background. Tested actually through the scene, the method obtains satisfactory localization effect. In the end of the paper, some experimental results are given out. In virtue of the successful car license plate detection and localization, it is possible for license plate number extraction and recognition.