1. A document server comprising a processor and for transmitting a document consisting of text only, wherein the document server is arranged to transmit the document to a terminal, and wherein the document contains or specifies a program executed before the terminal sends an image request based on image location information contained in the document to an image server in order for the terminal to request an image from the image server, for causing the terminal to function as: an additional information extractor that extracts from the document or from the program specified by that document, as additional information, characters or character strings that are to be overlaid as images on a background image, the characters or character strings being indicated at a position of a target for transformation by transformer; an image location information generator that generates image location information, wherein the image location information contains an image parameter that includes the extracted additional information and designates the background image, and wherein the additional information is overlaid as the images on the background image in an image generated by the image server; an over-writer that overwrites the image location information contained in the document with the image location information generated by the image location information generator; and an image request transmitter that transmits an image request to the image server in response to the document being loaded and the image location information being overwritten, and cause the image server to generate the image in response to receiving the image request, wherein the image request specifies the image parameter contained in the overwritten image location information, wherein the image server comprises: an image generator that generates, when the image designated by the image location information is requested by the terminal, the image in which the additional information designated by the image parameter contained in the image location information is overlaid as the images on the background image specified by the image parameter; and a transmitter that transmits the generated image to the terminal as response associated with the image request, and wherein: the image location information prior to being overwritten by the over-writer contains background information identifying the background image, the image location information generator generates the image location information containing the image parameter designating the background information contained in the image location information prior to being overwritten, and the image generator generates the image in which the additional information included in the image parameter contained in the image location information after being overwritten, is overlaid as the images on the background image identified by the background information.