1. A method for characterizing a shape of an object surface, comprising: acquiring image data including the object; analyzing the image data at a locus of points that are at a predetermined distance from a point of interest proximate to the object surface to determine which of the locus of points represents a foreground and which of the locus of points represents a background; and characterizing the shape of the object surface based on the characterization of the locus of points, wherein the step of characterizing the shape of an object surface based on the characterization of the locus of points includes: determining a longest continuous set of background points along the locus and a longest continuous set of foreground points along the locus, based on the analysis of the image data; and characterizing the shape of the object surface as convex, concave or flat based on the relative size of the determined longest continuous set of background points and the determined longest continuous set of foreground points.