13. A document layout analyzing method for analyzing layout of text on a document image to extract text blocks for character recognition purposes, comprising: storing a plurality of extraction conditions; extracting a first set of non-overlapping text blocks from the document image in accordance with one of the stored extraction conditions; extracting a second set of non-overlapping text blocks from the same document image in a different way from the first set, in accordance with another of the extraction conditions; performing character recognition on each extracted text block of the first and second sets; evaluating validity of each text block of the first and second sets, based on a result of the character recognition; creating a consolidation source set by finding a text block of the first set which overlaps with a text block of the second set, adding both of those text blocks to the consolidation source set, and repeating operations of finding a text block of the first and second sets which overlaps with any of the text blocks belonging to the consolidated set and adding the found text block to the consolidation source set; and producing a consolidated set of text blocks by selecting a most valid combination of non-overlapping text blocks from among the text blocks belonging to the consolidation source set, based on the validity of each text block that has been evaluated.
13. A document layout analyzing method for analyzing layout of text on a document image to extract text blocks for character recognition purposes, comprising: storing a plurality of extraction conditions; extracting a first set of non-overlapping text blocks from the document image in accordance with one of the stored extraction conditions; extracting a second set of non-overlapping text blocks from the same document image in a different way from the first set, in accordance with another of the extraction conditions; performing character recognition on each extracted text block of the first and second sets; evaluating validity of each text block of the first and second sets, based on a result of the character recognition; creating a consolidation source set by finding a text block of the first set which overlaps with a text block of the second set, adding both of those text blocks to the consolidation source set, and repeating operations of finding a text block of the first and second sets which overlaps with any of the text blocks belonging to the consolidated set and adding the found text block to the consolidation source set; and producing a consolidated set of text blocks by selecting a most valid combination of non-overlapping text blocks from among the text blocks belonging to the consolidation source set, based on the validity of each text block that has been evaluated. 16. The document layout analyzing method according to claim 13 , wherein said producing comprises: forming a plurality of combinations of non-overlapping text blocks from among the text blocks belonging to the consolidation source set and then evaluates the validity of each of the combinations, based on the result of the character recognition; and selecting text blocks belonging to one of the combinations that exhibits highest validity among others.