1. A data processing apparatus for managing a positional relationship among a plurality of cameras that are related to one another by performing image capturing so that each of the plurality of cameras captures an image of another one or more of the plurality of cameras, the data processing apparatus comprising: a captured image acquisition unit operable to acquire a plurality of different pieces of captured image data which have been captured by the plurality of cameras; an image recognition unit operable to perform image recognition processing on each of the pieces of captured image data to detect one or more predetermined pieces of detection target data each for identifying a captured camera, the captured camera being captured in the piece of captured image data which has been captured by a capturing camera, and the captured camera and the capturing camera being included in the plurality of cameras; a calculation unit operable to obtain, for each of the detected pieces of detection target data, by performing calculation based on the piece of detection target data, a piece of relative information indicating coordinates and a capturing direction of a position-specified camera in a coordinate system of an origin camera, the origin camera being one of the capturing camera and the captured camera, and the position-specified camera being an other one of the capturing camera and the captured camera; a judgement unit operable to judge, for each piece of relative information, whether the piece of relative information is to be converted to a piece of information which uses a coordinate system of a reference camera among the plurality of cameras; a relative information conversion operation unit operable to perform the conversion in accordance with a result of the judgement by the judgement unit; and a relative position information management unit operable to aggregate, (a) among the obtained pieces of relative information, each unconverted piece of relative information which uses the coordinate system of the reference camera, and (b) the converted pieces of relative information, thereby generating a piece of relative position information indicating coordinates and a capturing direction of each of the plurality of cameras in the coordinate system of the reference camera.