License plate extraction using adaptive threshold and line grouping

License plate recognition system is an essential tool for the Traffic Police Department and so, is widely being used for road traffic surveillance in many countries. This paper aims at locating the license plate in any given traffic surveillance image, by detecting the rectangle like shapes in that image. Line grouping algorithm extracts these shapes in the input image to locate the license plate. But its accuracy falls sharply for images where the license plate boundary suffers from occlusions leading to broken boundaries. The use of adaptive threshold and contours, instead of canny edge detector, to extract the line segments greatly increases the accuracy of line grouping algorithm, which is also verified by the results.