1. An image processing apparatus comprising: a reading control portion configured to read an image in a reading range including image regions of an entire document sheet image in both a state where a document sheet is not tilted and a state where the document sheet is tilted at a predetermined maximum tilt angle; a first blank sheet determination processing portion configured to be able to determine whether the image read by the reading control portion is a blank sheet image, based on an image of a first determination region which is included in both the image region of the entire document sheet image in the state where the document sheet is not tilted and the image region of the entire document sheet image in the state where the document sheet is tilted at the maximum tilt angle; and a first tilt correction processing portion configured to execute tilt correction processing for the document sheet image when the read image is not a blank sheet image, and execute no tilt correction processing for the document sheet image when the read image is a blank sheet image.