How bouncing light turns into a picture you can see
Every visible object sends out or scatters light. When that light reaches a flat mirror, the mirror sends it back in a predictable way: the light leaves the mirror at the same angle it arrived, measured from an imaginary line perpendicular to the glass [1]. Because the mirror preserves the pattern of incoming light, the light that reaches your eyes carries the same arrangement of colors and shapes as the scene in front of it. Your eyes focus that light, and you perceive a scene rather than a blur.
The key point is that the mirror does not store or project an image on its surface. It simply redirects light. The image you see is the result of your visual system interpreting redirected light as though it had traveled in a straight line from a source. That is why the reflection appears to be located behind the mirror, even though nothing is actually there [1][5].
Why the reflection seems to sit behind the glass
When you look into a plane mirror, the light reaching your eye follows a path that bends at the mirror surface. Your brain, however, assumes light travels in straight lines. To make sense of the incoming light, it traces the rays backward and places the apparent source at a point behind the mirror. This apparent source is called a virtual image: it looks real from your viewing position, but no light actually converges there [1].
This same principle is used when computers simulate mirrors. One approach models a mirrored viewpoint by imagining a camera placed behind the mirror and rendering the scene from that position, which reproduces the geometry of a plane mirror reflection [2]. The fact that a simulated camera behind the glass produces a convincing reflection supports the idea that the visible image is a geometric projection, not a physical object on the surface.
Why reflections are easy to get wrong
A mirror reflection is not just a copy of the scene. It must obey strict spatial rules: objects must appear at the correct position, at the correct angle, and with the correct proportions relative to the mirror's surface. When those rules are violated, reflections look subtly wrong. Generated images sometimes show reflections with positional offsets, misaligned directions, or distorted proportions, which are signs that the reflection geometry has not been enforced [3].
The fact that these errors are noticeable is itself evidence for how mirrors work. A correct reflection depends on the precise relationship between the object, the mirror surface, and the viewer. When a system gets that relationship right, the reflection looks physically plausible; when it does not, the image breaks the expectations set by real mirrors [3]. This reinforces that what you see in a mirror is a geometrically consistent redirection of light, not an arbitrary pattern.
What the mirror is not doing
It is tempting to think the mirror somehow captures or emits the image, but the evidence points to simple redirection of light. The mirror does not create new light or store the scene; it changes the direction of light that is already traveling toward it [1][5]. This is why a mirror in a dark room shows nothing: without light from objects in front of it, there is nothing to redirect.
One paper proposes a more speculative physical account involving photons transforming into antiphotons upon reflection, and links this to the left-right reversal of reflected objects [4]. That proposal is presented as a possible physical justification rather than an established explanation, and it is not needed to explain the everyday observation that a mirror shows what is in front of it. The straightforward account, supported by the reflection geometry described in the other papers, is that the mirror redirects light and your visual system interprets the redirected light as a scene behind the glass [1][2][5].
Sources used in this answer
Development of Augmented Reality Content for Preservice Teacher Education: Reflection of Light from a Plane Mirror
The paper describes how light reflects from a plane mirror and traces the path of reflected light starting from a point on the actual object, which relates to how mirrors create images.
Mirror-3DGS: Incorporating Mirror Reflections into 3D Gaussian Splatting
The paper models mirror reflections by simulating a mirrored viewpoint from behind the mirror using plane mirror imaging principles, producing realistic reflections in rendered scenes.
PhysReflect: Geometry and Perception Guided Diffusion for Physically-Plausible Mirror Reflections
The paper shows that generated mirror reflections often violate physical geometry through positional offsets, directional misalignment, and distortion, and that enforcing geometric and perceptual constraints improves physical plausibility.
On the Possible Harm of Photon Reflection by Mirrors and its Physical Justification
The paper proposes a speculative physical account in which photons reflecting from a mirror transform into antiphotons, and suggests this could relate to the left-right reversal of reflected objects.
Developing meaningful conceptual understanding in science
The paper discusses conceptual understanding in science, including that we see because light is reflected to our eyes, and uses how mirrors work as an example of a phenomenon to be explained.