1. A stereoscopic image aligning apparatus, comprising: an image pair obtaining unit configured to obtain an image pair including a left-eye image and a right-eye image that corresponds to the left-eye image; a corresponding point detecting unit configured to detect a corresponding point that represents a set of a first point and a second point, the first point being included in a first image that is one of the images of the image pair, and the second point being included in a second image that is the other of the images of the image pair and corresponding to the first point; a first matrix computing unit configured to compute a homography transformation matrix for transforming the first point such that a vertical parallax between the first point and the second point is smallest and an epipolar constraint is satisfied; a transforming unit configured to transform the first image using the homography transformation matrix; and an output unit configured to output a third image and the second image, the third image being the transformed first image.