In this invention, reading conditions for registration are determined in accordance with a document. This allows a user to read a document under recommended reading conditions without any special knowledge, and register the document in a predetermined server after performing anti-tampering processing on the document. For this purpose, a document is read by prescan in accordance with predetermined conditions, and information embedded in a predetermined marker in the read image data is extracted. On the basis of the extracted embedded information, reading condition information of the document is acquired. In accordance with the acquired conditions, the document is read by main scan. After that, at least one of electronic signature information and time stamp information is added to the image data obtained by the main scan. And the added image data are transmitted to and registered in a predetermined server on a network.