1. An image signature extraction device, comprising: a calculation unit that acquires a first extraction region and a second extraction region associated with each dimension, among a plurality of dimensions, calculates a first region feature associated with the first extraction region and a second region feature associated with the second extraction region, and calculates a difference value between the first region feature and the second region feature; a determination unit that determines a threshold for a quantization boundary based on a predetermined percentile rank in a distribution of the difference values of the plurality of dimensions; and a quantization unit that quantizes the difference value of each of the dimensions based on the threshold.