Why is a duplicate an “spitting image”?

Often if you look similar to someone, example your dad, people will say you look like a spitting image of your dad. But where does this weird expression come from, maybe it has a reference to spirit and image…No that’s to unrelated to be it. At the apex of the British empire, just about every manĀ  would spit in their boots to polish it. And the shine would reflect their face, that’s where the term originated.

Did you know in 1922 the British empire was one of the largest empires of all time, with a control over 458 million people and over 33 million km2 of lands in their possession.