1. A method for resolving an ambiguous character in a character string read by an OCR system, comprising: forming string permutations of the character string by substituting a plurality of replacement characters for the ambiguous character; deriving xgraphs from the string permutations; matching the xgraphs with a reference set of valid xgraphs; creating solution permutations by removing from the string permutations any string permutation containing an xgraph that does not match a valid xgraph in the reference set; and outputting the solution permutations.