1. An image processing apparatus comprising: one or more processors; and a memory coupled to the one or more processors, the memory having stored thereon instructions which, when executed by the one or more processors, cause the image processing apparatus to: detect, respectively from plural images obtained by imaging with plural imaging units a space in which plural persons exist, positions of the persons on the images; perform association of a same person in the plural images; estimate positions of the persons in the space, based on the positions of the persons on the images detected from the plural images and a result of the association; estimate eye directions of the persons, based on the plural images; estimate a spatial distribution of positions gazed by the plural persons, based on the estimated positions of the plural persons in the space and the estimated eye directions of the plural persons; and estimate a gazing level for each object, based on the estimated spatial distribution of the gazed positions.