1. An image processing apparatus generating image data of a document, comprising a processor, coupled to a memory, which functions as: an identifying area dividing unit configured to divide the image data into plural identifying areas; wherein said identifying area dividing unit will identify a first, second and third areas as part of the plural identifying areas; said first area comprising of a left edge part; said second area comprising of a bottom edge; said third area comprising of an internal area; a binarization processing unit configured to perform a binarization process for the identifying areas with respective binarization threshold values preset for the identifying areas; wherein the binarization threshold value of the first area is closer to the density value of black than the binarization threshold value of the second and third areas; a black pixel number identifying unit configured to identify whether or not the numbers of pixels with a density value of black in the respective identifying area exceed respective number threshold values preset for the identifying areas; and a blank sheet identifying unit configured to identify that the image data is image data of a blank sheet if the black pixel number identifying unit identifies that none of the numbers of pixels with the density value of black in the respective identifying areas exceeds the number threshold value.