In optics, a virtual image is an image in which the outgoing rays from a point on the object never actually intersect at a point. A simple example is a flat mirror where the image of oneself is perceived at twice the distance from yourself to the mirror. That is, if you're half a meter in front of the mirror, your image will appear at a distance of half a meter behind the mirror.
   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. A screen isn't necessary for the image to form.

• When we look through a diverging lens (at least one concave surface) or look into a convex mirror, what we see is a virtual image. However, if we observe a focused image on a screen behind a converging lens (at least one convex side) or in front of a concave mirror what we see on the screen is a real image because the image really is at the screen's location. If we position ourselves so that the screen is directly between ourselves and the optical device (mirror, lens, etc.), we can remove the screen and still observe the image. It is also important to note that a converging lens and concave mirror are also capable of producing virtual images if the object is within the focal length.