1. A method of determining an area or length of a three-dimensional feature on a compliant body part from a two-dimensional image thereof, comprising the steps of: (a) providing an imaging system for producing two-dimensional image coordinate data including intensity values at each pixel, respectively, of a two-dimensional image of the body part; (b) providing a transparent rigid body having a first major surface and an icon having a predetermined geometrical shape and lying in a plane having a predetermined relationship to the first major surface, the icon being on one of the first major surface and another surface having a predetermined relationship to the first major surface; (c) pressing the first major surface of the rigid body against a portion of the body part including the feature so as to flatten the feature to the first major surface; (d) operating the imaging system to produce a two-dimensional image of the feature and the icon; (e) determining a slant angle of the first major surface by measuring lengths of at least two axes in the two-dimensional image of the icon and computing a ratio between the axes, and measuring an area or length in the two-dimensional image of the feature outlined by a pointing device; and (f) correcting the area or length in the two-dimensional image of the feature in accordance with the slant angle of the body part at that pixel to obtain a corrected three-dimensional area or length.