Correcting for perspective? Because photographs are captured from a lens, distortion caused by the lens is often present. In traditional photography correction for perspective and distortion can be achieved when shooting with a view camera, tilt shift lens or post production software like Photoshop. When shooting with your device, perspective correction can easily be corrected by using an app like Perspective Correct.
In this first image, notice that the vertical lines in the image are leaning in or converging. Our eyes would not see this distortion in reality. In some photographs the distortion works but in others, it might be more aesthetically pleasing to remove it. In the second image, the vertical lines are now parallel to the edge of the frame once the perspective correction has been applied.