1. A processing apparatus comprising: a receiving unit that receives an image data group including a plurality of pieces of image data corresponding to a plurality of images respectively; a specifying unit that specifies an object included in each image based on a piece of image data in the image data group received by the receiving unit; a setting unit that automatically sets, for each object, correlation information specifying a correlation between objects specified by the specifying unit; a first determining unit that determines target object information specifying a target object; a second determining unit that determines information specifying a second object having a correlation with the target object, based on the target object information determined by the first determining unit and the correlation information set by the setting unit; and an extraction unit that extracts one or more of the plurality of the pieces of image data including the target object and one or more of the plurality of the pieces of image data including the second object from the image data group based on the target object information determined by the first determining unit and the information determined by the second determining unit.