Final answer:
The unseen image in the image receptor before processing is known as the latent image. It becomes visible after the image receptor undergoes processing, distinguishing it from a real image which can be projected, or a virtual image, which cannot.
Step-by-step explanation:
The "unseen" image that is contained in the image receptor (IR) before it is processed is called the latent image. A latent image is formed when the imaging plate is exposed to x-rays or light, and it stores the image in a non-visible form. Once the image receptor is processed, typically via scanning in digital radiography or chemical development in analog film radiography, the latent image is converted into a visible image that can be viewed and interpreted by radiologists or technicians.
The term real image refers to an image wherein light rays from one point on the object actually cross at the location of the image and can be projected onto a screen, a piece of film, or the retina of an eye. In contrast, a virtual image is formed on the opposite side of the lens from where the object is placed and is not a type of image that can be captured on an image receptor before processing.