1. A data processing apparatus for identifying whether first image data was generated by a predetermined image generating apparatus, comprising: a light receiving unit configured to receive respective light on respective light receiving elements, the light receiving elements including an aperture, wherein different apertures vary in shape and cause distinctive variations in a light receiving sensitivity of the light receiving elements; a correlation detection unit configured to detect variations in a non-zero amount of light striking different light receiving elements, the different light receiving elements having distinctive variations in light receiving sensitivity due to the different aperture shapes; and an identifying unit configured to identify whether said first image data was generated using said image generating apparatus based on said correlation detected by said correlation detecting section, wherein the correlation detection unit is configured to cut out first subset image data from reference image data based on a first cutout position, to cut out second subset image data from the first image data based on a second cutout position shifted with respect to the first cutout position, and to detect a correlation between the first subset image data and the second subset image data.