1. An image processing apparatus that determines a priority ranking of a subject detected from an image, the image processing apparatus comprising: a detection unit that detects one or more subjects from an image; a computation unit that computes a priority for determining a priority ranking, for each of the subjects detected by the detection unit; and a determination unit that determines the priority ranking of each of the subjects detected by the detection unit, based on the priority computed by the computation unit, wherein the computation unit: assigns a larger weight to a subject detected by the detection unit at least one of when the subject has a larger size and/or when the subject is positioned nearer a center of the image; corrects the assigned weight by a larger weight when a most recent priority ranking determined for the subject by the determination unit in a previous image from which the subject is detected is higher; computes a higher priority for the subject when the corrected weight is larger; and, when a predetermined condition is satisfied, computes the priority with a reduced amount of correction by the weight of the most recent priority ranking.