1. An image processing apparatus comprising: a superimposition processing unit configured to perform a blending process for a plurality of continuously captured images, wherein the superimposition processing unit is configured to selectively input luminance signal information of a RAW image or a full color image as a processing target image and perform a superimposition process, and performs a process for sequentially updating data that is stored in a memory for storing two image frames so as to enable superimposition of any desired number of images; and wherein the superimposition processing unit includes: a global motion vector calculation unit configured to calculate a global motion vector of a plurality of continuously captured images; a positioning processing unit configured to generate a motion compensated image in which a subject position of a reference image is positioned at a position of a key image in accordance with the global motion vector; a moving subject detection unit configured to obtain moving subject information on the basis of a pixel difference between corresponding pixels of the motion compensated image obtained as a result of positioning of the positioning processing unit and the key image; and a blending processing unit configured to blend the key image and the motion compensated image on the basis of the blending ratio based on the moving subject information so as to generate a superimposed image.