Why is an image from a double convex lens sometimes inverted?

An image from a double convex lens is sometimes inverted because the lens causes the light rays to cross over (converge) at a point called the focal point. When the object is placed beyond the focal point, the light rays that pass through the lens converge to a point behind the lens, forming an inverted image. This is in contrast to the case when the object is placed within the focal point, in which case the light rays diverge after passing through the lens, forming an upright (non-inverted) image.

In summary, the inversion of the image occurs when the object is placed beyond the focal point of a double convex lens, as the converging light rays cross over before forming the image.