In optics, a virtual image is an image in which the outgoing rays from a point on the object always diverge. It will appear to converge in or behind the optical device (i.e., a mirror). A simple example is a flat mirror where the image of oneself is perceived at twice the distance from oneself to the mirror. That is, if one is half a meter in front of the mirror, one's image will appear to be at a distance of 1 meter away (or half a meter inside or behind the mirror). Because the rays never really converge, one cannot project a virtual image.

By contrast, a real image is an image in which the outgoing rays from a point on the object pass through a single point. It is easiest to observe real images when projected on an opaque screen (although a screen is not necessary for the image to form).