1. An image data providing server that communicates via a network with an external device, and that provides image data to the external device, comprising: an electronic album storage unit configured to store a plurality of image data received from a user terminal and to store the received plurality of image data as an album in association with an album identification; a generation unit configured to generate a disclosure album ID for the album corresponding to the plurality of image data stored in the electronic album storage unit by a) generating a first check digit by performing a predetermined check digit generation process utilizing the album identification stored in the electronic album storage unit in association with the album, and b) adding the generated first check digit to the album identification, the generated disclosure album ID being constituted by the album identification and the first check digit; a issuing unit configured to issue the generated disclosure album ID to the external device; a receiving unit configured to receive, from the external device, a request for browsing an album stored in the electronic album storage unit, the request including a disclosure album ID; a computing unit configured to a) extract an album identification from the received disclosure album ID, b) to compute a second check digit by applying the predetermined check digit generation process to the extracted album identification contained in the received disclosure album ID and c) to obtain a resultant ID by adding the second check digit to the album identification contained in the received disclosure album ID; a comparing unit configured to compare the obtained the resultant ID with the received disclosure album ID; a determining unit configured to determine whether or not the received disclosure album ID is proper, and determines that the received disclosure album ID is proper in a case where a result of the comparison by said comparing unit indicates that the obtained resultant ID coincides with the received disclosure album ID, and otherwise determines that the received disclosure album ID is not proper; a first transmission unit configured to, in a case where the determining unit determines that the received disclosure album ID is not proper, transmit display data of an error window to the external device; a search controlling unit configured to control a search unit to search the electronic album storage unit, utilizing the extracted album identification, for image data associated with an album identification corresponding to the extracted album identification contained in the received disclosure album ID, in a case where the result of the determination by the determining unit indicates that the received disclosure album ID is proper; an image data obtaining unit configured to obtain the image data from the electronic album storage unit in a case where the search unit finds an album identification corresponding to the extracted album identification stored in the electronic album storage unit; a second transmission unit configured to transmit, to the external device, display information for displaying the image data obtained from the electronic album storage unit by the image data obtaining unit; and a third transmission unit configured to transmit, to the external device, display data of an error window in a case where the search unit does not find an album identification corresponding to the extracted album identification stored in the electronic album storage unit.