A thumbnail distribution system includes a client device and a server communicatable with each other by using a hyper text transfer protocol (HTTP). A client device includes a request generating unit, a request transmitting unit, a response receiving unit, and a data processing unit. The request generating unit generates an HTTP request having a request line storing a file name of a file store in a storing unit. The request transmitting unit transmits the HTTP request. The response receiving unit receives an HTTP response having a response body storing a thumbnail corresponding to the file having the file name stored in the request line. The data processing unit performs a data processing based on the thumbnail stored in the response body. The request receiving unit receives the HTTP request transmitted from the request transmitting unit. The response generating unit generates the HTTP response based on the HTTP request. The response transmitting unit transmits the HTTP response to the response receiving unit.