1. A non-transitory computer-readable medium configured to store a computer program that performs a method of detecting a road sign in an image for development of a navigation database, the method comprising: receiving a plurality of images of roads, the plurality of images captured via a camera mounted on a vehicle; determining gradient vectors of one or more features in each of the plurality of images, the gradient vectors being substantially invariant to scale, rotation, and illumination of the one or more features, the gradient vectors determined as a function of a scale-invariant feature transform; comparing the determined gradient vectors with reference gradient vectors to determine whether a road sign is included in at least one of the plurality of images, the reference gradient vectors corresponding to a text character; comparing distances between the determined gradient vectors to identify a cluster of features corresponding to a series of text including the text character; and identifying at least one of the plurality of images determined to include the road sign as a function of the series of text determined from the gradient vectors of the cluster of features, the reference gradient vectors, and a dictionary of possible road sign text.