1. An information processing method comprising: making a video-image selection for cyclically acquiring at least two types of video images; making a mask determination for selecting, for each acquired video image, a mask pattern for masking the acquired video image by replacing some pixels composing the acquired video image with pixels of a single color such that said some pixels are spatially removed; and displaying on a display unit the video image after replacing said some pixels composing the video image with pixels of a single color based on the selected mask pattern, wherein, in the mask determination, when selecting a mask pattern for a certain video image, a mask pattern is selected that is different from a mask pattern used for the last video image, the mask pattern being different in the position of pixels not to be replaced with pixels of a single color, wherein in the mask determination, a mask pattern is determined based on the resolution of the acquired video image, and wherein in the mask determination, if the resolution of the acquired video image in the vertical direction is higher than that in the horizontal direction, a mask pattern that has a periodicity in the vertical direction of the video image is selected, and if the resolution of the acquired video image in the vertical direction is lower than that in the horizontal direction, a mask pattern that has a periodicity in the horizontal direction of the video image is selected.