1. An image forming apparatus comprising: a scanner configured to generate image data by reading a region including a first surface of an original document and a region including a second surface of the original document, respectively, in a state in which regions other than the first and second surfaces of the document are respectively read with low luminance; a processor configured to: determine, from a first image data which was generated by the scanner reading a first surface of the original document, a region other than a first document region corresponding to the first surface of the original document using a difference in luminance in the first image data, wherein a region with low luminance in the first image data is determined to be the region other than the first document region, eliminate the region other than the first document region from the first image data, determine, from a second image data which was generated by the scanner reading a second surface of the original document, a region other than a second document region corresponding to the second surface of the original document using a difference in luminance in the second image data, wherein a region with low luminance in the second image data is determined to be the region other than the second document region, eliminate the region other than the second document region from the second image data, and generate, for printing on a single surface of a recording medium, a printing image including: the first read image with the region other than the first document region eliminated, and the second read image with the region other than the second document region eliminated; and a printer configured to print the generated printing image on a single surface of a recording medium.