1. An image processing apparatus which is equipped with an imaging device of imaging an imaging region in which an original document can be put and a displaying device capable of displaying an image, the image processing apparatus comprising: an extracting unit configured to extract, from an image obtained by imaging with the imaging device the imaging region in which the original document has been put, original image data indicating an image of the original document; a remaining image displaying unit configured to cause the displaying device to display a remaining image which is generated from the original image data extracted by the extracting unit and corresponds to the image of the original document, at a position where the original document was put; a detecting unit configured to detect that the original document enters a detecting region for detecting the original document; and a thumbnail image displaying unit configured to, in response to the detection by the detecting unit that the original document enters the detecting region, cause the displaying device to display a thumbnail image of the remaining image such that the thumbnail image does not overlap the original document which enters the detecting region.