Systems, methods, and software consistent with the present invention use combinations of two or more letters (xgraphs) or characters, such as three letter combinations (trigraphs), to aid in deciphering ambiguous characters in OCR systems. Embodiments consistent with the invention compare possible xgraphs constructed by substitution for the ambiguous OCR-read character(s) to a reference set of xgraphs. The reference set of xgraphs contains predetermined valid xgraphs, which may be ranked by preference. If a possible xgraph matches a reference xgraph, then the ambiguous character(s) are resolved in favor of the characters in the reference xgraph. Embodiments may also use the context of the ambiguous character string to aid in resolving the ambiguity where more than one possible solution exists.