1. An image processing system comprising: a component marked with a feature whose position and attitude relative to an imaging device can be specified by being imaged by the imaging device; and an image processing apparatus connected to the imaging device, the image processing apparatus comprising: a captured image acquisition unit for acquiring a captured image captured by the imaging device; a feature detection unit for detecting the feature from the captured image; a reference acquisition unit for acquiring a position/attitude reference based on the detected feature, the reference being used as a reference for indicating a position and attitude in a space imaged by the imaging device; and a relative relation information acquisition unit for acquiring, based on the captured image from which the feature is detected in plurality, relative relation information indicating a relative relation in position and attitude among the plurality of position/attitude references acquired for the respective features.