1. An image processing apparatus, comprising: an extraction unit configured to extract a plurality of feature points respectively having a local feature amount from an inputted image, and image region information related to the plurality of feature points; and a registration unit configured to register an association between at least one target feature point of the plurality of feature points and another one of the feature points as an index of the inputted image, if a relational degree with a region denoted by the image region information of the target feature point is above a threshold value.