1. An image processing determining apparatus comprising: an external device outputting display data including an image; an edge extracting unit configured to extract a plurality of edges indicating the outline of an object in the image included in the display data output from the external device with lines; an edge selecting unit, configured to select certain edges from the plurality of edges extracted by the edge extracting unit, by a certain selection method; an edge image generating unit, configured to generate an edge image composed of the certain edges selected by the edge selecting unit; and a display unit displaying the edge image generated by the edge image generating unit, wherein the edge selecting unit selects the certain edges by the selection method matched with characteristics of the external device.