1. A non-transitory storage medium storing a plurality of instructions executable by a computer of a display device comprising an image taking device and a display, the plurality of instructions, when executed by the computer, causing the display device to perform: controlling the display to display a real-space image which is being taken by the image taking device; determining whether the real-space image taken by the image taking device includes a marker; synthesizing the real-space image and a content associated with the determined marker when it is determined that the real-space image includes the marker; controlling the display to display the real-space image synthesized with the content; receiving an instruction for keeping displaying the content on the display while the real-space image synthesized with the content is displayed on the display; controlling the display to display the real-space image with the synthesized content on the display when the instruction is not received and when the real-space image taken by the image taking device includes the marker; controlling the display to display the real-space image with the synthesized content on the display when the instruction is received and when the real-space image taken by the image taking device does not include the marker; and controlling the display to disappear the content on the display while displaying the real-space image when the instruction is not received and when the real-space image taken by the image taking device does not include the marker.