1. A character recognition method performed by a character recognition device, comprising the steps of: receiving information in which a device identifier, character image data, and a corrected character code are associated with one another, storing the received information as a new entry in a correction history table, deciding whether or not information of each entry included in the correction history table satisfies a predetermined condition, extracting a plurality of character image data pieces from the entries included in the correction history table according to a result of the decision, producing new character image data by performing difference detection on the extracted character image data, and storing, in an additional table, information in which the new character image data, a character code, and a device identifier are associated with one another, deciding whether or not the additional table has a device identifier received with a character recognition instruction when receiving information in which the device identifier and character image data are associated with each other as well as the character recognition instruction, performing character recognition based on the additional table when it is decided that the additional table has the device identifier received with the character recognition instruction, and performing character recognition, when it is decided that the additional table does not have the device identifier received with the character recognition instruction, based on a basic table storing an entry in which predetermined character image data and a character code are associated with each other.