1. A method for comparing an input image of an unknown face with a reference image of a known face, comprising the steps of: extracting a feature vector from each image; compressing the feature vectors into compressed feature vectors; and comparing the compressed feature vectors to determine a similarity score for the two faces, in which n is a number of features in each feature vector, v=[f 1 , f 2 ,. .. , f n ] is the feature vector extracted from each image, f i is an i th feature of the feature vector v x where 1≦i≦n, μ=[μ 1 , μ 2 ,. .. , μ n ] is a vector of means of the features, σ=[σ 1 ,σ 2 ,. .. , σ n ] is a vector of standard deviations of the features, s is a scalar constant controlling a width of a truncation region about μ, and the compressing further comprises: determining a value F i for each extracted feature value f i according to T i = 2 b - 1 × ( 1 + ( f i - μ i s ⁢ ⁢ σ i ) ) , ⁢ C i = { 2 b - 1 for ⁢ ⁢ T i > 2 b - 1 T i for ⁢ ⁢ 0 ≤ T i ≤ 2 b - 1 , 0 for ⁢ ⁢ T i < 0 ⁢ ⁢ F i = truncate ⁡ ( C i ). where b is a number of bits used to store the value F i .