In this situation, which is how people generally interpret the static image, the yellow square lies in front of the red one. Wherever they overlap, the yellow image occludes, or conceals, the image of the red square. This suggests that the yellow square is closer than the red. Occlusion only tells us the relative depth of objects. We can't determine how much farther away the red sqaure is, only that it is farther. But hey, whenever you are trying to solve an impossible problem, all hints help!