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 apparatus to: acquire an image from a first image capturing unit and a second image capturing unit; detect a first object and a second object in the image; associate detection results of the first object and the second object; store a positional relationship between respective fields of view of the first image capturing unit and the second image capturing unit; estimate a three-dimensional position of the first object based on the positional relationship and the first object detected in respective images captured by the first image capturing unit and the second image capturing unit; and estimate a three-dimensional position of the second object based on the three-dimensional position of the associated first object.