1. An image processing apparatus, comprising: a character recognizing unit configured to identify a character image in a document image; a font matching unit configured to determine a character code and a font type corresponding to the identified character image; a fore-and-background setting unit configured to set the document image as a background image and set a standard character image based on the determined character code and the determined font type as a foreground image; and a background image correcting unit configured to (a) delete a deletion area in the background image, the deletion area taking a same position as the character image or the standard character image, (b) interpolate a differential area between the character image and the standard character image in a specific neighborhood area that contacts with the deletion area on the basis of the background image, and (c) interpolate the deletion area on the basis of the back ground image; wherein (c1) if the deletion area is an open area that is partially surrounded with an object included in the background image and has a part not surrounded with an object included in the background image, then the background image correcting unit determines intersection points between a boundary of the object and a boundary of the deletion area as endpoints, connects a pair of two of the endpoints with a straight line or a curved line and thereby changes a shape of the deletion area, and interpolates the deletion area on the basis of the background image after changing the shape of the deletion area; and (c2) if the deletion area is a closed area that is completely surrounded with an object included in the background image, then the background image correcting unit interpolates the deletion area on the basis of the background image.