An image processing apparatus comprising: a feature point detection unit configured to detect feature points from both images of a first image and a second image, which are images of ranges of a paper document, wherein the ranges of the images are different from each other, wherein the first image and the second image include overlap areas where a part of the paper document is comprised in the first image and in the second image, wherein there is a color difference between the paper document and the outside of the paper document, and wherein no feature point is detected outside the paper document; a feature point matching unit configured to extract feature points corresponding to each other between the feature points detected from both images of the first image and the second image by the feature point detection unit, wherein the extracted feature points are feature points corresponding to each other extracted between the feature points detected from the overlap areas of the both images; a vanishing point detection unit configured to detect vanishing points of a plane to which the paper document belongs from each of the images; a transformation parameter derivation unit configured to derive transformation parameters for image combining; and an image combining unit configured to combine the first image and the second image by using the derived transformation parameters, characterized by an edge extraction unit configured to extract edges corresponding to each other from both images, wherein the extracted edges are i) edges of a paper end of the paper document or ii) edges of a paper end of the paper document and edges of a straight line included in the paper document in the same direction as the paper end; wherein the edge extraction unit is further configured to rearrange at least two extracted feature points in each of the first image and the second image to points having the coordinates of intersections of straight lines connecting each of the extracted feature points and the detected vanishing point in the direction perpendicular to the edge of the paper end, and the extracted edges; and the transformation parameter derivation unit is further configured to derive the transformation parameters for image combining by using four coordinates of feature points which are the feature points on the intersections after the rearrangement and, in case less than four feature points were rearranged, by using the feature points before rearrangement additionally to the feature points on the intersections after the rearrangement. a feature point detection unit configured to detect feature points from both images of a first image and a second image, which are images of ranges of a paper document, wherein the ranges of the images are different from each other, wherein the first image and the second image include overlap areas where a part of the paper document is comprised in the first image and in the second image, wherein there is a color difference between the paper document and the outside of the paper document, and wherein no feature point is detected outside the paper document; a feature point matching unit configured to extract feature points corresponding to each other between the feature points detected from both images of the first image and the second image by the feature point detection unit, wherein the extracted feature points are feature points corresponding to each other extracted between the feature points detected from the overlap areas of the both images; a vanishing point detection unit configured to detect vanishing points of a plane to which the paper document belongs from each of the images; a transformation parameter derivation unit configured to derive transformation parameters for image combining; and an image combining unit configured to combine the first image and the second image by using the derived transformation parameters, characterized by an edge extraction unit configured to extract edges corresponding to each other from both images, wherein the extracted edges are i) edges of a paper end of the paper document or ii) edges of a paper end of the paper document and edges of a straight line included in the paper document in the same direction as the paper end; wherein the edge extraction unit is further configured to rearrange at least two extracted feature points in each of the first image and the second image to points having the coordinates of intersections of straight lines connecting each of the extracted feature points and the detected vanishing point in the direction perpendicular to the edge of the paper end, and the extracted edges; and the transformation parameter derivation unit is further configured to derive the transformation parameters for image combining by using four coordinates of feature points which are the feature points on the intersections after the rearrangement and, in case less than four feature points were rearranged, by using the feature points before rearrangement additionally to the feature points on the intersections after the rearrangement.