1. An image processing apparatus comprising: a storage; and a CPU that is configured to: acquire a position and a size of a target photographic subject in an original image acquired by image capturing: generate mask information indicating a relation between (i) a position to be subjected to predetermined image processing in the original image and (ii) a strength of the predetermined image processing, based on the acquired position and the acquired size of the target photographic subject; and generate a new image by performing predetermined image processing of a different strength on different positions in the original image by using the generated mask information; wherein: the storage stores basic information of the mask information, the CPU generates the mask information by using the basic information stored in the storage, the basic information stored in the storage includes a basic shape of a processing area that is subjected to the predetermined image processing, and the basic information stored in the storage includes information regarding a change in the strength of the predetermined image processing in the processing area that is subjected to the predetermined image processing, the information regarding the change in the strength indicating that the strength is changed to be gradually increased from a center side to a periphery side.