A communication device selects image data to be transmitted to a public network from image data stored in an imaging device, inputs a character string, converts the file name of image data received from the imaging device into the input character string, and transmits the image data to the public network. Upon reception of a request for image data from the public network, the communication device converts the file name of the requested image data into the file name received from the imaging device, and requests transmission of the image data from the imaging device.