1. A method comprising: obtaining an image comprising license plate information; dividing the image into a plurality of sub-blocks; computing a spatial activity measure for each sub-block of the plurality of sub-blocks; determining an activity threshold; determining that a sub-block of the plurality of sub-blocks is an active sub-block by comparing the spatial activity measure for the sub-block with the activity threshold; generating, using one or more processors, a second image of the license plate information, wherein the second image comprises the active sub-block; and obtaining the license plate information based on the second image.