A display apparatus (100, 101) comprising: a display configured to display an image; a video signal reception unit configured to receive a first video signal from an image source; a peripheral device interface to which an external peripheral device is connectable, the external peripheral device providing an image signal corresponding to a second video signal or a graphic signal; a video processor configured to process the first video signal received through the video signal reception unit and the second video signal input through the peripheral device interface from the external peripheral device; an image composing module; and a controller configured to: control the video processor to process the first video signal; determine an output route of the image signal input through the peripheral device interface, depending on a kind of the image signal; in response to identifying that the image signal input from the external peripheral device through the peripheral device interface is the graphic signal, output directly the graphic signal input from the external peripheral device to the image composing unit, and control the image composing module to combine a graphic image corresponding to the graphic signal with a first video image corresponding to the processed first video signal so that the display displays a combined image comprising the graphic image and the first video image; and in response to identifying that the image signal input from the external peripheral device through the peripheral device interface is the second video signal, output the second video signal to the video processor, and control the video processor to process the second video signal so that the display displays a second video image corresponding to the processed second video signal. a display configured to display an image; a video signal reception unit configured to receive a first video signal from an image source; a peripheral device interface to which an external peripheral device is connectable, the external peripheral device providing an image signal corresponding to a second video signal or a graphic signal; a video processor configured to process the first video signal received through the video signal reception unit and the second video signal input through the peripheral device interface from the external peripheral device; an image composing module; and a controller configured to: control the video processor to process the first video signal; determine an output route of the image signal input through the peripheral device interface, depending on a kind of the image signal; in response to identifying that the image signal input from the external peripheral device through the peripheral device interface is the graphic signal, output directly the graphic signal input from the external peripheral device to the image composing unit, and control the image composing module to combine a graphic image corresponding to the graphic signal with a first video image corresponding to the processed first video signal so that the display displays a combined image comprising the graphic image and the first video image; and in response to identifying that the image signal input from the external peripheral device through the peripheral device interface is the second video signal, output the second video signal to the video processor, and control the video processor to process the second video signal so that the display displays a second video image corresponding to the processed second video signal. control the video processor to process the first video signal; determine an output route of the image signal input through the peripheral device interface, depending on a kind of the image signal; in response to identifying that the image signal input from the external peripheral device through the peripheral device interface is the graphic signal, output directly the graphic signal input from the external peripheral device to the image composing unit, and control the image composing module to combine a graphic image corresponding to the graphic signal with a first video image corresponding to the processed first video signal so that the display displays a combined image comprising the graphic image and the first video image; and in response to identifying that the image signal input from the external peripheral device through the peripheral device interface is the second video signal, output the second video signal to the video processor, and control the video processor to process the second video signal so that the display displays a second video image corresponding to the processed second video signal.