In a data transmission apparatus and method of the present invention, a specific operator ID for an operator who uses a data processing device to process image data to be copied or transmitted, is selected. Specific owner IDs for owners who are authorized to access the image data, are selected. User identification data, inclusive of all operator IDs and owner IDs correlated to the data processing device, are stored in a storage device each time image data is captured by the data processing device. Allocation of the stored user identification data to each of the image data is managed by reading items of the user identification data from the storage device in response to the selections of the specific operator ID and the specific owner IDs and displaying the user identification data items.