A display apparatus comprising: a display; an optical sensor comprising a plurality of light transmitters and a plurality of light receivers arranged around the display, facing each other and configured to transmit and obtain light; and a processor configured to: identify a touch position of a pointer on a screen of the display, based on light transmitted and obtained by the optical sensor, identify a touch size of the pointer, based on light transmitted and obtained by the optical sensor, and cause the display to display an image corresponding to the identified touch size on the screen along touch positions of successive touches, based on movement of the pointer, characterized in that the processor is configured to identify the number of pixels corresponding to the identified touch size of the pointer, based on a size and a resolution of the display, and adjust a width of at least a portion of the image displayed on the screen of the display based on the identified number of pixels, and wherein the processor is further configured to: based on a real-time variable touch-size mode being selected, cause the display to display an image of which a width is varied corresponding to variation in the identified touch size of the pointer on the screen along touch positions of successive touches while the pointer is moved, based on a fixed touch-size mode being selected, cause the display to display an image with a width fixed corresponding to an initial touch of successive touches on the screen along touch positions of successive touches while the pointer is moved. a display; an optical sensor comprising a plurality of light transmitters and a plurality of light receivers arranged around the display, facing each other and configured to transmit and obtain light; and a processor configured to: identify a touch position of a pointer on a screen of the display, based on light transmitted and obtained by the optical sensor, identify a touch size of the pointer, based on light transmitted and obtained by the optical sensor, and cause the display to display an image corresponding to the identified touch size on the screen along touch positions of successive touches, based on movement of the pointer, characterized in that the processor is configured to identify the number of pixels corresponding to the identified touch size of the pointer, based on a size and a resolution of the display, and adjust a width of at least a portion of the image displayed on the screen of the display based on the identified number of pixels, and wherein the processor is further configured to: based on a real-time variable touch-size mode being selected, cause the display to display an image of which a width is varied corresponding to variation in the identified touch size of the pointer on the screen along touch positions of successive touches while the pointer is moved, based on a fixed touch-size mode being selected, cause the display to display an image with a width fixed corresponding to an initial touch of successive touches on the screen along touch positions of successive touches while the pointer is moved. identify a touch position of a pointer on a screen of the display, based on light transmitted and obtained by the optical sensor, identify a touch size of the pointer, based on light transmitted and obtained by the optical sensor, and cause the display to display an image corresponding to the identified touch size on the screen along touch positions of successive touches, based on movement of the pointer, characterized in that the processor is configured to identify the number of pixels corresponding to the identified touch size of the pointer, based on a size and a resolution of the display, and adjust a width of at least a portion of the image displayed on the screen of the display based on the identified number of pixels, and wherein the processor is further configured to: based on a real-time variable touch-size mode being selected, cause the display to display an image of which a width is varied corresponding to variation in the identified touch size of the pointer on the screen along touch positions of successive touches while the pointer is moved, based on a fixed touch-size mode being selected, cause the display to display an image with a width fixed corresponding to an initial touch of successive touches on the screen along touch positions of successive touches while the pointer is moved. based on a real-time variable touch-size mode being selected, cause the display to display an image of which a width is varied corresponding to variation in the identified touch size of the pointer on the screen along touch positions of successive touches while the pointer is moved, based on a fixed touch-size mode being selected, cause the display to display an image with a width fixed corresponding to an initial touch of successive touches on the screen along touch positions of successive touches while the pointer is moved.