A method for emphasizing differences in graphical appearances between an original document and a modified document is provided in accordance with an aspect of the present invention. The method includes the step of receiving a first bitmap of the modified document, and a second bitmap of the original document. The method includes deriving a set of difference points based upon a comparison of the first bitmap and the second bitmap. The method includes a step of superposing a spatial index onto the set of difference points, and generating polygon vertices from a plurality of adjacent elements of index. Each of the elements has a predetermined density of difference points. The method concludes with generating an annotation from the polygon vertices.