1. A marker detecting system 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, selecting as a unique feature an image feature that does not appear in said background video image based on said extracted feature, and detecting a marker generated based on said unique feature, comprising: storage unit for storing a feature of said marker; and feature checking unit for checking a feature in the video image subjected to detection, which contains said marker in an environment in which detection of a marker is performed, with that of said marker, and notifying detection of a marker when a match of the features is found.