Cellular phones (1a, 1b) adjust the brightness of an image before sending mail with an attached photograph, so that it is possible to visually verify the mail text when the mail text is overlaid over the image, which serves as a background image attached to the mail text at the receiving side, after which the mail is send to a system (in particular, to mail servers (33) and (63)). The color of mail text characters is changed in responsive to the image brightness. When the cellular phones (1a, 1b) receive an e-mail with an attached photograph, they display the mail text overlaid over the image as a background image (which has had its brightness adjusted).