An image input/output system which makes it possible to reduce a load on a server in the case of using a network scan function in a server based computing environment. An image input/output system comprises a multifunction peripheral, a server, and a computer which are communicably connected to one another via a network. The server receives a reading instruction from the computer and instructs the multifunction peripheral to read an original according to the reading instruction. In the multifunction peripheral, a reader section reads the original based on the instruction from the server, and a control section sends thumbnail image data obtained by the reader section to the computer without going through the server.