What is the origin of the idiom "spitting image" and when to use it?

The origin of the idiom "spitting image" is unclear, but several theories exist. One possibility is that it originated from the phrase "spirit and image," which referred to someone closely resembling a deceased family member or ancestor. Over time, the phrase evolved into "spitting image." Another theory suggests that "spit" in this context refers to the likeness or resemblance being so vivid that it appears as if the person or thing has been "spit out" as an exact copy. Figuratively, this expression is used to describe someone who bears a striking resemblance to another person, often in terms of physical appearance.