1. An image processing apparatus comprising: a processor configured to execute; an extractor configured to receive sheet image data that is generated by reading an image on a medical record sheet onto which basic medical information and encoded information representing the basic medical information are printed, and extract, from the sheet image data, information image data representing a portion where the basic medical information is printed; an image generator configured to generate reference image data representing the basic medical information, based on the encoded information represented in the sheet image data; a detector configured to detect a correction that is to be performed on the basic medical information printed on the medical record sheet, based on a difference between the information image data and the reference image data; a decoding unit configured to generate decoded information by decoding the encoded information; and an image reproducing unit configured to reproduce the reference image data from the decoded information in accordance with an expression condition to be used for comparison with the information image data.