A method of identifying the direction of characters in an image block, comprising: performing optical character recognition processing on the image block by assuming various directions as assumed character directions, respectively, to obtain sub image blocks, recognized characters corresponding to the sub image blocks and correctness measures thereof in each of the assumed character directions; in sub image blocks in two assumed character directions with a 180° mutual relation therebetween, searching for minimum matching pairs of the sub image blocks sequentially from corresponding sides of the two assumed character directions, wherein a minimum matching pair is two sets of adjacent sub image blocks that are adjacent sub image blocks in the assumed character directions with a 180° mutual relation therebetween, wherein any one of the two sets of sub image blocks of the minimum matching pair, after being rotated by 180° along with the entire image block, will superimpose upon the other set of the two sets of sub image blocks of the minimum matching pair and the two sets of sub image blocks include a minimum number of sub image blocks; determining whether there is one sub image block in each of the two assumed character directions in a minimum matching pair and recognized characters corresponding to the two sub image blocks belonging to the minimum matching pair are the same rotation invariant character or belong to the same rotation invariant character pair recorded in a lexicon of characters with rotation invariant characteristic and when there is one sub image block in each of the two assumed character directions in a minimum matching pair and recognized characters corresponding to the two sub image blocks belonging to the minimum matching pair are the same rotation invariant character or belong to the same rotation invariant character pair recorded in a lexicon of characters with rotation invariant characteristic, adjusting the correctness measures corresponding to the two sub image blocks to the same numerical value, wherein the rotation invariant character comprises a character with a spin symmetry of 180°, i.e., the rotation invariant character becomes itself after being rotated by 180°, and wherein the rotation invariant character pair comprises two characters, any one of which becomes consistent with or has a high similarity in shape to the other one after being rotated by 180°; calculating an accumulative correctness measure in each of the assumed character directions based on the potentially adjusted correctness measures; and identifying the direction of the characters in the image block according to the accumulative correctness measures. performing optical character recognition processing on the image block by assuming various directions as assumed character directions, respectively, to obtain sub image blocks, recognized characters corresponding to the sub image blocks and correctness measures thereof in each of the assumed character directions; in sub image blocks in two assumed character directions with a 180° mutual relation therebetween, searching for minimum matching pairs of the sub image blocks sequentially from corresponding sides of the two assumed character directions, wherein a minimum matching pair is two sets of adjacent sub image blocks that are adjacent sub image blocks in the assumed character directions with a 180° mutual relation therebetween, wherein any one of the two sets of sub image blocks of the minimum matching pair, after being rotated by 180° along with the entire image block, will superimpose upon the other set of the two sets of sub image blocks of the minimum matching pair and the two sets of sub image blocks include a minimum number of sub image blocks; determining whether there is one sub image block in each of the two assumed character directions in a minimum matching pair and recognized characters corresponding to the two sub image blocks belonging to the minimum matching pair are the same rotation invariant character or belong to the same rotation invariant character pair recorded in a lexicon of characters with rotation invariant characteristic and when there is one sub image block in each of the two assumed character directions in a minimum matching pair and recognized characters corresponding to the two sub image blocks belonging to the minimum matching pair are the same rotation invariant character or belong to the same rotation invariant character pair recorded in a lexicon of characters with rotation invariant characteristic, adjusting the correctness measures corresponding to the two sub image blocks to the same numerical value, wherein the rotation invariant character comprises a character with a spin symmetry of 180°, i.e., the rotation invariant character becomes itself after being rotated by 180°, and wherein the rotation invariant character pair comprises two characters, any one of which becomes consistent with or has a high similarity in shape to the other one after being rotated by 180°; calculating an accumulative correctness measure in each of the assumed character directions based on the potentially adjusted correctness measures; and identifying the direction of the characters in the image block according to the accumulative correctness measures.