1. An image processing apparatus comprising processing circuitry configured to: select from a plurality of diffusion-weighted images with different applied directions of a motion probing gradient magnetic field pulse or different diffusion sensitive coefficients, a diffusion-weighted image that conforms to a predetermined condition; register the selected diffusion-weighted image with a reference image for which the diffusion sensitive coefficient being set to a reference value to correct the selected diffusion-weighted image; and register the corrected diffusion-weighted image with each of the other diffusion-weighted images of the plurality of diffusion-weighted images to correct each of the other diffusion-weighted images.