An image processing apparatus comprises a first estimation unit configured to estimate a deformation between a first image and a second image under a first condition and obtain first deformation information; a second estimation unit configured to estimate a deformation between the first image and the second image under a second condition different from the first condition and obtain second deformation information; and an obtaining unit configured to obtain one of an estimation error and reliability of the deformation at a point on an image based on a difference between the first deformation information and the second deformation information.