The simplest way to differentiate a real image from a virtual image is to determine whether it can be projected onto a screen. These two types of images are also differentiated from each other based on the image’s position in relationship to the lens and the object, by its size in relationship to the object and by its vertical orientation.
If the viewer puts a screen in the focal plane of a real image, the image appears on the screen as in a cinema or with an overhead projector. Though a virtual image is visible to the naked eye, the image cannot be projected onto a screen. This is because the lens bends rays of light, and where these bent rays intersect, an image is created.
When a real image is created, the light rays travel through the lens and intersect on the other side. When a screen is placed at that intersection, an image appears on the screen. The light rays for a virtual image intersect on the same side of the lens as the object, but no light ever moves along these paths. Also, a virtual image appears smaller than the object, while a real image appears larger. Finally, a real image appears upside down and a virtual image appears upright.