A real image is the collection of focus points actually made by converging rays, while a virtual image is the collection of focus points made by extensions of diverging rays. In other words, it is an image which is located in the plane of convergence for the light rays that originate from a given object.

How do you know if an image is real?

A real image occurs where rays converge, whereas a virtual image occurs where rays only appear to diverge. Real images can be produced by concave mirrors and converging lenses, only if the object is placed further away from the mirror/lens than the focal point, and this real image is inverted.

Can you tell by looking whether an image is real or virtual?

How can you tell (by looking) whether an image formed by a single lens or mirror is real or virtual? Virtual image cannot be projected on a screen. You cannot distinguish a real image from a virtual image simply by judging from the image perceived with your eye.