A transmission-side information terminal displays a marker whose wavelength changes with time on the basis of a tag ID acquired from a management server. A receiving-side information terminal takes an image to acquire the tag ID, and transmits storage instruction information to a distribution server, the storage instruction information including the tag ID, an area number indicating a position of the receiving-side information terminal and image data acquired by taking an image. The image distribution server stores the tag ID, the area number and the image data in the storage instruction information in association with one another. The transmission-side information terminal transmits query information including the tag ID acquired from the management server and the area number indicating its own position to the image distribution server, thereby acquiring image data associated with the tag ID and the area number from the image distribution server.