1. A method for optically recognizing alphanumeric characters comprising: a) storing polygonal outer contours and inner contours of reference characters and their relative geometrical positions as normalized reference curves transformed into a tangent space; b) optically scanning an outer contour and inner contours of a character to be recognized and transforming scanned data into binary data; c) approximating the outer contour and the inner contours of the character to be recognized as a polygon, normalizing straight line segments of the polygon and transforming the normalized straight line segments into a tangent space to generate character curves; d) comparing the character to be recognized to the reference characters in a rotation-invariant manner by shifting at least the character curve of the outer curve and the reference curves of the outer contours relative to each other in the tangent space until a surface area enclosed by the character curve and a given reference curve is at a minimum; e) using the surface area between the character curves for the outer contour and the inner contours of the character to be recognized and respective reference curves for outer contours and the inner contours of the reference characters as a measure of the extent to which the character and the reference characters differ; and f) selecting the reference character which yields the smallest surface area between the character curves and the reference curves as the recognized character.