1. An image processing apparatus comprising: an image input unit configured to input an image of a plurality of objects; an orientation estimation unit configured to estimate each of a plurality of orientations of a plurality of picking target objects included in the plurality of objects based on the image; an occurrence likelihood storage unit configured to store an occurrence likelihood corresponding to each of the orientations that the objects can have; an occurrence likelihood obtaining unit configured to obtain each occurrence likelihood for each of the plurality of orientations of the plurality of picking target objects by referring to the occurrence likelihood storage unit, wherein each occurrence likelihood represents a likelihood of occurrence of each of the plurality of orientations; a reliability obtaining unit configured to obtain a reliability for each estimated orientation of the plurality of picking target objects, based on the obtained occurrence likelihood, wherein the obtained reliability increases as the obtained occurrence likelihood increases; a comparison unit configured to compare the obtained reliabilities of the plurality of picking target objects; and a selection unit configured to select an object, among the plurality of picking target objects, to be picked by a picking unit, based on the comparison of the obtained reliabilities of the plurality of picking target objects, wherein the image input unit, the orientation estimation unit, the occurrence likelihood obtaining unit, the reliability obtaining unit, comparison unit, and the selection unit are implemented by a processor and a memory.