1. A method for identifying an object in an electronically acquired image that includes at least one two-dimensional array of pixels, comprising: (a) identifying a plurality of one-dimensional gradient runs oriented along a common direction in the two-dimensional array of pixels; wherein each of the one-dimensional gradient runs includes three or more adjacent pixels (P 1. .. P k ) oriented along the common direction; wherein each of the one-dimensional gradient runs is defined by a common set of brightness trend parameters that include at least one brightness difference threshold (T) and a brightness difference direction parameter selected from the group comprising increasing brightness or decreasing brightness; wherein first and second adjacent pixels (P 1 , P 2 ) along each one-dimensional gradient run have a brightness difference that is greater than the threshold (T) and a difference direction that matches at least one the brightness difference direction parameter of the one-dimensional gradient run; and wherein each subsequent pixel (P n , n>1) after the first pixel (P 1 ) in each one-dimensional gradient run has a succeeding neighbor (P n+1 ) oriented immediately after the pixel (P n ) along the common direction such that each adjacent pair of pixels (P n , P n+1 , n>1) along each of the one-dimensional gradient runs has a difference that is unchanging or that matches the brightness difference direction parameter of the one-dimensional gradient run; (b) forming a second-order set of gradient runs by selecting a group of one-dimensional gradient runs identified in step (a); wherein each of the one-dimensional gradient runs in the group has a pixel that is offset along an axis perpendicular to the common direction from a pixel in a neighboring one-dimensional gradient run in the group; and wherein each of the one-dimensional gradient runs in the group has at least one pixel that is immediately adjacent to a pixel in another one-dimensional gradient run in the group; and (c) identifying the object in the array using the second-order set of gradient runs.