A communication system includes a server device and a client device. The server device includes an encoding unit that encodes information about characters contained in a first image to generate an encoded image, a generation unit that generates a second image in which the generated encoded image is embedded at a position specified from a position of the characters on the first image in place of the characters, and a transmission unit that transmits the second image to the client device in response to a request for the first image from the client device. The client device includes an extraction unit that extracts the encoded image from the received second image, a decoding unit that decodes the extracted encoded image, and a replacement unit that replaces the encoded image on the second image with characters specified from decoded information to generate the first image.