1. An image processing apparatus comprising: an image acquiring unit configured to acquire an image from a first image capturing unit and a second image capturing unit; a detection unit configured to detect a first object and a second object in the image; an association unit configured to associate detection results of the first object and the second object; a storage unit configured to store a positional relationship between respective fields of view of the first image capturing unit and the second image capturing unit; a first estimation unit configured to 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 a second estimation unit configured to estimate a three-dimensional position of the second object based on the three-dimensional position of the first object associated by the association unit.