1. A coordinate-conversion-parameter determination apparatus comprising: an image capture unit that generates a first image by photographing, at a first place, a marker that is placed in advance and whose position and shape are known and a second image by photographing, at a second place different from the first place, the marker; a marker detector that detects feature points of the marker from each of the first image and the second image; a three-dimensional position determiner that calculates three-dimensional coordinates of each of the feature points of the marker in a camera coordinate system in which reference is the first place, based on a position of the feature point in the first image and a position of the feature point in the second image; and a coordinate-conversion-parameter determiner that calculates a coordinate conversion parameter so that a sum of absolute values of errors between three-dimensional coordinates in a world coordinate system, the three-dimensional coordinates in the world coordinate system being obtained by converting the three-dimensional coordinates of the feature points of the marker in the camera coordinate system by using the coordinate conversion parameter, and three-dimensional coordinates of feature points in the world coordinate system that correspond to the feature points of the marker in real space is minimized.