In an image processing apparatus, display on a display device connected to the image processing apparatus is controlled. A change in an image to be displayed on the display device is detected. If a change in the image to be displayed has been detected, controlling to transmit not an entire area of the image to be displayed but a partial area including a changed area in image to be displayed. If a method of transmitting an image to a projection apparatus is a first communication method where a reception response is not made to the transmission of the image, controlling to transmit the partial area and to periodically transmit the entire area.