1. An image processing apparatus comprising: a calculation unit configured to detect feature points from an image included in a first image group, and to calculate a local feature amount of each feature point using pixels adjacent to the feature point; a comparison unit configured to determine similarity between images based on local feature amounts of the detected feature points for each combination of images included in the first image group; a separation unit configured to separate an image, which is included in the first image group and corresponds to the combination having the similarity not less than a first threshold, as an image of a second image group; a selection unit configured to select a reference image from the second image group based on the similarity of images of the second image group; a detection unit configured to detect, for each feature point of the reference image, a number of images included in the second image group, each of which has a feature point corresponding to the feature point of the reference image, as a number of corresponding images; and an estimation unit configured to estimate an object region based on a distribution of feature points, each of which has the number of corresponding images exceeding a second threshold, in the reference image, wherein at least one of the calculation unit, the comparison unit, the separation unit, the selection unit, the detection unit, or the estimation unit is implemented by using a processor.