1. A marker generating system, comprising: feature extracting unit for extracting as a feature a segment containing a distinctive pattern in a background video image not containing a marker in an environment in which detection of a marker is performed; feature storage unit for calculating and storing a frequency distribution of said extracted features; unique feature selector for selecting as a unique feature a portion having a frequency equal to or smaller than a predefined value from said frequency distribution of the features; and marker generator for generating a marker based on said unique feature.