A real image is produced by an optical system (a combination of lenses and/or mirrors) when light rays from a source cross to form an image. Light rays diverge from the real image in the same way that they diverge from the source. A real image can be seen by placing a screen at the image location, or it can be turned into a virtual image that can be viewed directly with the aid of a second lens or mirror.
The diagram below shows the principle light rays leaving a source to create a real image on the opposite side of the convex lens. Compared to the original source, the real image is inverted. For a convex lens, a real image will occur whenever the source is further from the lens than the focal length.