PURPOSE: To improve recognition of optical symbols in plural classes having plural versions.

CONSTITUTION: Each image in a library is so weighted that V×L comparisons are constituted for each input pixel version in each symbol to minimize the degree of risk of confusion. The spread pixel version is divided into subclasses furthermore, and pairs of first comparisons C* and second comparisons C** is determined in L comparisons among each of V comparisons, and recognition margins between pairs of comparisons are determined, and a pair of comparison C1* and comparison C1** having a minimum recognition margin Mi* are selected to determine a corresponding pair of pixel images Ij* and Ij**. A certain pixel of the closest pixel image Ij* or the second closest pixel image Ij** is weighted to increase the recognition margin Mi* between them. This processing is repeated until the library of pixel images (and sub-images) becomes a library of emphasized symbol templates (and subtemplates).