I too had heard "spirit and image" and furthermore heard it attributed to African American speech before it entered the general speech, consistent with the poster's identification of a probable southern origin. From an "Occam's Razor" approach this seems most likely – it doesn't require invoking bizarre slang for spitting or employing outdated language forms as an explanation. It is also very easy to hear how the shortened form could have arisen in general speech. Finally, this phrase also clearly implies similarity in both character and appearance, consistent with the sense of common usage.