This lecture explains the positioning of objects and images in relation to a lens. Starting with the object's position before the lens, the instructor demonstrates how to calculate the precise image position using the thin lens formula. Through examples with a diverging lens, the lecture covers the concept of virtual images and how they are formed. The instructor also illustrates how an image can become an object when passing through a lens in the opposite direction, resulting in a virtual image. The lecture concludes with a numerical calculation to determine the final position of the virtual image, emphasizing the importance of understanding the principles of lens positioning.