1. A method of displaying an image, the method being performed by a processor and comprising: displaying a main image in a display area of a display device; generating, at an image generator, an auxiliary image configured to induce eye blinking of a user; combining, at a display controller, the main image and the auxiliary image; and displaying, at the display device, the combined image in a first area corresponding to a portion of the display area, wherein the position of the first area varies periodically by randomly determining the position of the first area and setting a time limit, wherein the combining is performed by using a first material image which includes at least a portion of the main image and a second material image which is the auxiliary image, wherein the combining comprises at least partially overlapping the second material image on the first material image, wherein a transparency of each pixel of the second material image is determined based on a pixel value of the second material image, wherein when pixel values of a first portion of the second material image are lower than pixel values of a second portion of the second material image, a first transparency is set to the first portion of the second material image and a second transparency higher than the first transparency is set to the second portion of the second material image, wherein when the pixel values of the first portion of the second material image are higher than the pixel values of the second portion of the second material image, the second transparency is set to the first portion of the second material image and the first transparency is set to the second portion of the second material image, and wherein the combining is performed by applying a preset predetermined weight to the pixel value of the second material image to generate a weighted pixel value and averaging a sum of the weighted pixel value and a pixel value of the first material image.