1. A method for detecting an aperture of a graphical representation of an ear impression comprising the steps of: determining a first plurality of contour lines on a surface of said graphical representation; determining a difference value for each contour line in said first plurality of contour lines, said difference value a function of the difference between a first value of a characteristic of each contour line and a second value of said characteristic of an adjacent contour line; and identifying the contour line in said first plurality of contour lines having a greatest value of said difference value.