The present invention provides an image processing apparatus which processes a scanned image in which a document image is shown, and includes a reliability determining section and a display control section. The reliability determining section determines reliability of coincidences of respective first through fourth directions with a first reference direction, the first through fourth directions being perpendicular to or reverse to each other, the first reference direction being an upward direction of the document image. The display control section creates markers indicating the respective first through fourth directions, and causes a display device to display a preview image in which the markers and the scanned image overlap each other. Further, the display control section causes the markers to be displayed in respective different ways by changing respective densities in accordance with the reliability.