1. A pattern recognition apparatus comprising: an extracting section for extracting, from a query image that is composed of at least one piece of pattern component and previously undergoes a geometric transformation, the pattern component; a feature acquiring section for acquiring a geometric invariant feature of the pattern component as a query feature, the query feature being represented by at least three feature points including first, second and third feature points, each feature point located on the pattern component and being retrieved from the pattern component based on a predetermined rule; a comparing section for comparing the query feature with a plurality of reference features, each reference feature representing different reference patterns prepared as candidates for pattern recognition; and a pattern determination section for determining, as a recognition result, a specific reference pattern out of the candidates based on a similarity of features therebetween and, wherein: each reference feature is represented using feature points retrieved from each reference pattern based on the same rule as that of the query feature, and based on the predetermined rule, a position of the first feature point is specified out of points which are located on the pattern component and are invariant to the geometric transformation, a position of the second feature point is specified using a characteristic regarding a shape of the pattern component, the characteristic being invariant to the geometric transformation, and a position of the third feature point is specified from a predetermined value being invariant to the geometric transformation and from the specified positions of the first and second feature points.
1. A pattern recognition apparatus comprising: an extracting section for extracting, from a query image that is composed of at least one piece of pattern component and previously undergoes a geometric transformation, the pattern component; a feature acquiring section for acquiring a geometric invariant feature of the pattern component as a query feature, the query feature being represented by at least three feature points including first, second and third feature points, each feature point located on the pattern component and being retrieved from the pattern component based on a predetermined rule; a comparing section for comparing the query feature with a plurality of reference features, each reference feature representing different reference patterns prepared as candidates for pattern recognition; and a pattern determination section for determining, as a recognition result, a specific reference pattern out of the candidates based on a similarity of features therebetween and, wherein: each reference feature is represented using feature points retrieved from each reference pattern based on the same rule as that of the query feature, and based on the predetermined rule, a position of the first feature point is specified out of points which are located on the pattern component and are invariant to the geometric transformation, a position of the second feature point is specified using a characteristic regarding a shape of the pattern component, the characteristic being invariant to the geometric transformation, and a position of the third feature point is specified from a predetermined value being invariant to the geometric transformation and from the specified positions of the first and second feature points. 10. A pattern recognition apparatus according to claim 1 , wherein the query image includes a word pattern composed of plural characters, and the pattern recognition apparatus further includes: a word candidate determining section for obtaining the shortest route in which each character recognized by the pattern determining section is traced once, and for determining an order and inverse order of the obtained route as candidates of the word; a rotation angle determining section for obtaining a rotation angle of each character in a predetermined direction of the query image; and a reading-order determining section in which a difference in the rotation angle between two characters adjacent to each other along the order or inverse order of the route is specified as a first evaluation index, the rotation angle that the first character should take is estimated based upon the direction toward a second character, which is adjacent to a first character that is defined to be either one end of each candidate, and a predetermined rule involved with a reading direction, and the difference between the estimated rotation angle and the rotation angle of the first character determined by the rotation angle determining section is specified as a second evaluation index, wherein the candidate that minimizes the first and second evaluation indexes is selected in order to determine a reading order of characters constituting the word.