In each of personal computers, information concerning an application software to process image data sent to a scanner is received. A dialog box is displayed and a user entry is made as to whether transmission is permitted or not. When transmission is rejected by the user, a notice of the rejection of transmission is given to the scanner. When transmission is permitted by the user, the application software is started and a notice of the permission of transmission is given to the scanner. Then, image data is received from the scanner and processed by the started application software.