1. An image processing device that performs image processing on a composite image obtained by merging a first image and a second image having different exposure conditions, the image processing device comprising: a data acquiring unit that acquires the composite image and region data indicating a target region of the composite image; and an image processing unit that performs different image processes between the target region and a region other than the target region based on the region data, wherein the first image and the second image comprise a moving subject region on which a moving subject is rendered, the composite image is generated by using a pixel value selected by using a first mask that selects pixel values having lower luminance values between the first image and the second image or a second mask that selects pixel values having higher luminance values between the first image and the second image in the moving subject region, the region data represents one or a plurality of regions generated based on the moving subject region of the composite image, as the target region, and in a case where the moving subject region is generated by using the first mask, the image processing unit performs a tone mapping process in which a luminance value is not increased to be equal to or greater than a first threshold value.