1. An image processing apparatus generating image data of a document, comprising: an identifying area dividing unit configured to divide the image data into plural identifying areas; a binarization processing unit configured to perform a binarization process for the identifying areas with respective binarization threshold values preset for the identifying 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.