An image processing apparatus , comprising: a projection control unit configured to perform control such that a first pattern image in which a plurality of first feature points are arranged is caused to be projected on a projection surface , and a second pattern image being a part of the first pattern image and including a plurality of second feature points (200, 200a-200i) corresponding to respective first feature points is caused to be projected on a planar part of said projection surface; an acquisition unit configured to acquire, from a photographing unit , a first photographed image of the projected first pattern image projected on the projection surface, said first photographed image having a distorted shape due to said projection surface, and a second photographed image of the second pattern image projected on the planar part of said projection surface; an extraction unit configured to extract second connected components (L2, L2a, L2b, L2c) in which the second feature points in the second photographed image are connected in a predetermined direction, and first connected components (L1f) in which first feature points in the first photographed image including positions corresponding to the second feature points included in the second connected components are connected in said predetermined direction; a shift amount calculation unit configured to calculate shift amounts (H) of the first connected components with respect to the second connected components; and a first calculation unit configured to calculate first correction information for correcting a projection target image on the basis of the shift amounts. a projection control unit configured to perform control such that a first pattern image in which a plurality of first feature points are arranged is caused to be projected on a projection surface , and a second pattern image being a part of the first pattern image and including a plurality of second feature points (200, 200a-200i) corresponding to respective first feature points is caused to be projected on a planar part of said projection surface; an acquisition unit configured to acquire, from a photographing unit , a first photographed image of the projected first pattern image projected on the projection surface, said first photographed image having a distorted shape due to said projection surface, and a second photographed image of the second pattern image projected on the planar part of said projection surface; an extraction unit configured to extract second connected components (L2, L2a, L2b, L2c) in which the second feature points in the second photographed image are connected in a predetermined direction, and first connected components (L1f) in which first feature points in the first photographed image including positions corresponding to the second feature points included in the second connected components are connected in said predetermined direction; a shift amount calculation unit configured to calculate shift amounts (H) of the first connected components with respect to the second connected components; and a first calculation unit configured to calculate first correction information for correcting a projection target image on the basis of the shift amounts. <EOS>