11. A recognition confidence measurement system comprising: at least one processor to control one or more of the following units; a phoneme string extraction unit detecting a feature vector of an input speech signal through normalization of a histogram and extracting a phoneme string from the feature vector of the input speech signal; a candidate extraction unit obtaining information about a distance between a phoneme string of the input speech signal and a phoneme string of a predetermined vocabulary, by a predetermined phoneme confusion matrix which sets the distance to be decreased in proportion to the increase of a matching degree between phonemes, extracting as candidates the phoneme string of the vocabulary that has a higher similarity and that has a comparatively shorter distance from the speech signal, from a predetermined dictionary; a distance estimation unit estimating a lexical distance between the extracted candidates, the estimating of the lexical distance comprising performing a dynamic matching of a pair of candidates selected from the extracted candidates; and a registration determination unit determining whether the input speech signal is an in-vocabulary, based on the lexical distance, wherein the dynamic matching comprises: for each phoneme in a first candidate of the selected pair of candidates, determining as a first matching pair the phoneme in the first candidate and the corresponding phoneme in a second candidate of the selected pair of candidates and determining as a second matching pair the phoneme in the first candidate and a phoneme having an identical shape to the phoneme in the first candidate; wherein the estimating of the lexical distance further comprises: calculating a score for the pair of candidates; and estimating the lexical distance using the calculated score; wherein the calculating of the score calculates the score using the phoneme confusion matrix.
11. A recognition confidence measurement system comprising: at least one processor to control one or more of the following units; a phoneme string extraction unit detecting a feature vector of an input speech signal through normalization of a histogram and extracting a phoneme string from the feature vector of the input speech signal; a candidate extraction unit obtaining information about a distance between a phoneme string of the input speech signal and a phoneme string of a predetermined vocabulary, by a predetermined phoneme confusion matrix which sets the distance to be decreased in proportion to the increase of a matching degree between phonemes, extracting as candidates the phoneme string of the vocabulary that has a higher similarity and that has a comparatively shorter distance from the speech signal, from a predetermined dictionary; a distance estimation unit estimating a lexical distance between the extracted candidates, the estimating of the lexical distance comprising performing a dynamic matching of a pair of candidates selected from the extracted candidates; and a registration determination unit determining whether the input speech signal is an in-vocabulary, based on the lexical distance, wherein the dynamic matching comprises: for each phoneme in a first candidate of the selected pair of candidates, determining as a first matching pair the phoneme in the first candidate and the corresponding phoneme in a second candidate of the selected pair of candidates and determining as a second matching pair the phoneme in the first candidate and a phoneme having an identical shape to the phoneme in the first candidate; wherein the estimating of the lexical distance further comprises: calculating a score for the pair of candidates; and estimating the lexical distance using the calculated score; wherein the calculating of the score calculates the score using the phoneme confusion matrix. 13. The system of claim 11 , wherein the registration determination unit determines the input speech signal as in-vocabulary, when the calculated score satisfies a set numerical value and determines the input speech signal as an out-of-vocabulary, when the calculated score does not satisfy the set numerical value.