A control device includes a receiver, a generator, and a controller. The receiver receives a shared image to be shared with a user from a poster through a communication line. The generator generates a presented image, the presented image being an image that is to be presented to the user and that is obtained by processing the shared image such that the image is different from the shared image received by the receiver. The controller performs control to transmit the presented image to the poster through the communication line to notify the user of content of the shared image.