A method for emphasizing differences in graphical appearances between an original document and a modified document using annotations with outer and inner boundaries is disclosed. A first bitmap of the modified document and a second bitmap of the original document are received. A set of difference points is derived from a comparison of the first bitmap and the second bitmap. Those difference points are representative of coordinates within the first and second bitmaps having pixel value differences exceeding a predetermined threshold. An outer boundary and an inner boundary of the difference points is derived, then an annotation defined by an area between the outer boundary and the inner boundary is generated.