In optics, real images can be projected onto a screen, while virtual ones always remain behind mirrors. This apparently straightforward distinction is based on complex premises which emerged in the Early Modern period, and its development went hand in hand with a transformation of the notion of image, which became detached from sensual perception. In this article I will outline this historical process, and argue that the distinction between a real and virtual image still implies a reference to visual perception (...) which makes it problematic, yet useful for didactic purposes. (shrink)