1. An image processing apparatus comprising: a holding unit configured to hold a positional relationship of a plurality of image capturing units; an acquisition unit configured to detect objects from respective images captured by the plurality of image capturing units and acquire positions of the objects on the captured images and geometric attributes of the objects; an associating unit configured to associate the detected objects, based on the positional relationship, the positions, and the geometric attributes; and an estimation unit configured to estimate a three-dimensional position of the objects based on the positional relationship and the positions of the detected objects.