1. An image processing apparatus, comprising: a background density distribution estimating part that estimates density distribution of pixels in a background area in an image to be processed; an area density distribution estimating part that estimates density distribution in a designated area in the image; and an entry existence judging part that judges existence or not of entry of predetermined information in the designated area, based on the density distribution of the pixels in the background area estimated by said background density distribution estimating part and the density distribution in the designated area estimated by said area density distribution estimating part.