To realize a display image sharing system which can show an expression on a shared display even if a corresponding application is not installed in a host device without necessitating the conversion by a user of a file and restricting the user to a specific file format.

The display image sharing system is the client-host type one. In this case, when a file transmitted from a client cannot be opened, the file conversion to a file format is requested to the client, and a server in which the file exists and its name are transmitted from the client. When the file thus transmitted cannot be opened, the file conversion is requested to the server. In either case, when the files can be opened, display is made without the conversion.