1. An image processing apparatus comprising: at least one memory configured to store instructions; and at least one processor connected to the at least one memory and configured to execute the instructions to: obtain a plurality of images that are generated by repeating to photograph images with exposure values different for every predetermined step while changing a photographing target area continuously; detect an overlapped area among the plurality of images; compute composition ratios of the overlapped areas of the plurality of images according to signal value of at least one of the plurality of images and the exposure values of the plurality images; and generate a wide angle-composite image by compositing the plurality of images based on the composition ratios, wherein the at least one processor executes further instruction to: when compositing another image onto the generated wide-angle composite image to generate a new wide-angle composite image, not use the another in an area where a predetermined number of images are used for compositing the plurality of images, from among the overlapped areas where the another image and the generated wide-angle composite image overlap each other, but use the another image in an area where images of which number is less than the predetermined number are used for compositing the plurality of images, from among the overlapped areas.