An image processing apparatus is disclosed including a document data analysis unit and an authentication unit. The document data analysis unit can identify policy data related to the authentication of a document based on information related to a document and/or the type of the document, identify items in document data to be verified, conversion to be performed on data of the items, and verification information contained in the document data based on the identified policy data, and perform the identified conversion on data of the identified items. The authentication unit can authenticate the document based on the data on which the identified conversion is performed and the identified verification information.