1. An image processing apparatus comprising: a unifying unit that unifies images of identification target regions cut out from a learning image for which a state on whether or not an identification target object is included is already known to a predetermined fixed size; a memory that stores a learning model which is generated based on feature information extracted from images of the identification target regions that have been unified to the fixed size by the unifying unit and used for determining a probability that the target object is included in the images; a storing unit that stores identification target images converted into images of different image sizes; a setting unit that sets a position and a size of a candidate region which is likely to include an identification target object of an identification target image; a selecting unit that selects, in a case where the candidate region at the position and of the size set by the setting unit is cut out from the identification target images of the different image sizes stored in the storing unit, an identification target image of an image size with which the size of the cut-out candidate region is closest to the fixed size to which the images of the identification target regions are unified when the learning model is generated; an extracting unit that extracts, from the identification target image of the image size selected by the selecting unit, feature information indicating a feature of the image of the candidate region at the position and of the size set by the setting unit; and a determining unit that determines a target object included in the image of the candidate region, based on the feature information extracted by the extracting unit and the learning model stored in the memory.