1. A method for detecting an edge of a document being scanned, comprising: (a) scanning a portion of the document against a substantially light reflecting backing to obtain a first set of image data; (b) scanning a portion of the document against a substantially light absorbing backing to obtain a second set of image data; (c) calculating a set of first values from the first set of image data, each one of the first values being a first-order statistic; (d) calculating a set of second values from the second set of image data, each one of the second values being a first-order statistic; and (e) determining a detected edge of the document from the set of first values and the set of second values.