1. An image processing device which creates a depth map using a multi-view image, the image processing device comprising: a detection unit configured to detect one or more features in each of images included in the multi-view image, by performing edge detection or corner detection on the multi-view image; a derivation unit configured to derive, as corresponding points, a pair of the features corresponding to each other between the images included in the multi-view image, based on similarity in feature quantity of the detected features; a calculation unit configured to calculate, based on the derived corresponding points, a reliability of a correspondence between the images included in the multi-view image in preparation for creating the depth map; a creation unit configured to create the depth map using the correspondence between the images included in the multi-view image when the calculated reliability is a first reliability, and create the depth map without using the correspondence between the images included in the multi-view image when the calculated reliability is a second reliability which is lower than the first reliability; and a transformation unit configured to calculate, using at least four of the derived corresponding points, a transformation parameter for projective transformation of a first image included in the multi-view image into a second image included in the multi-view image, and transform the first image using the transformation parameter, wherein: the detection unit is configured to detect an edge as the feature, and the calculation unit is configured to calculate the reliability which is higher when an error of the first image resulting from the projective transformation with respect to the second image is smaller, and calculate the error of the first image resulting from the projective transformation with respect to the second image, by calculating a difference in pixel values only from a region where the detected edge has a strength above a threshold value in the second image.