1. A method for detecting regions in an image, the method comprising: detecting, by one or more computing devices, a set of regions of the image that include features that appear to correspond to objects of a particular type; and identifying, by the one or more computing devices, a given region of the set of regions as not including features that correspond to objects of the particular type based on at least information describing a ratio including a size of the given region and a dimension of a feature included within the given region, wherein the information describing the ratio includes a dimension corresponding to a height of a camera that captured the image.