My conception of a two dimensional image is of an object with its sides, its front and its back. The only example I can think of is of a mirror's reflection (assuming that photons are not particles and therefore have no depth). We can now mimic anything we see with a mirror, a high definition screen TV, or a painting on a canvas (in theory though it is a 3D image). It follows that the only visual perception we have of any object is the refraction and reflection of photons on its surface and our only way to prove that what we see has depth (forming a 3rd dimension) is our examination through an extra sense (touch). Our brain then uses sight to perceive the world around us in two dimensions and uses the knowledge obtained from touch to come to the conclusion that what we are seeing has depth. Furthermore, if photons do exist only in 2 dimensions, then our perception of any object is a two dimensional image at different time intervals. If what I am saying is correct ( and I would appreciate anyone who would correct my view otherwise), then our problem understanding a fourth dimension is based on our state of consciousness. We still have appreciate the meaning of seeing in three dimensions.