1. An image processing apparatus to reduce a scattered-ray component from a radiographic image, the image processing apparatus comprising: a memory storing a program; one or more processors configured to execute the program; an acquiring unit configured to acquire a radiographic image using a radiation detector that detects a radiation through an object; a scattered-ray estimating unit configured to estimate a scattered-ray component contained in the radiographic image, wherein the scattered-ray component originates from a scattered ray which is a radiation scattered in the object; a scattered-ray reducing unit configured to reduce the scattered-ray component from the radiographic image; and an identifying unit configured to attach identification information for identifying the scattered-ray component to the radiographic image, wherein, in a case where a reduction process performed by the scattered-ray reducing unit for reducing the scattered-ray component corresponding to the identification information is different from a reduction process performed by the scattered-ray reducing unit for reducing the scattered-ray component from a radiographic image newly acquired by the acquiring unit, the scattered-ray estimating unit newly estimates a scattered-ray component contained in the radiographic image without using the estimated scattered-ray component corresponding to the identification information, and wherein the acquiring unit, the scattered-ray estimating unit, the scattered-ray reducing unit, and the identifying unit are implemented by the one or more processors.