1. An image processing apparatus comprising: a processor configured to act as: an image acquisition unit that acquires first image data representing a first image and second image data representing a second image that is an image acquired by performing additional recording on the first image; a region specifying unit that specifies a region, where additional recording is performed with respect to the first image, of the second image in accordance with the first image data and the second image data acquired by the image acquisition unit; and a partial-image recognition unit that recognizes a partial image recorded in the region specified by the region specifying unit, wherein the region specifying unit compares the first and second images to generate a difference image, and specifies the region where additional recording is performed on the difference image and specifies the corresponding region on the first image, wherein the partial-image recognition unit determines whether to perform character recognition on the corresponding region of the first image or the specified region of the difference image based on whether the corresponding region on the first image is blank, wherein when the partial-image recognition unit determines that the corresponding region on the first image is not blank, the partial-image recognition unit performs character recognition in the region on the first image instead of performing character recognition in the specified region of the difference image, and wherein when the partial-image recognition unit determines that the corresponding region on the first image is blank, the partial-image recognition unit performs character recognition in the specified region of the difference image instead of performing character recognition in the region of the first image.