Ok, there are actually two questions here.
I remember seeing the Zeitgeist movie where the narrator stated something like that the Zodiac is on of the oldest the oldest conceptual images in human history while displaying the classical image of the Zodiac on the screen (the circle divided into twelve sections where each section has an associated sign. Example.
I guess the original image originates from Babylon.
Not discussing the accuracy of the movie in general ;)
The questions:
Thank you in advance!
It depends on how you define the "zodiac." If you mean by that a division of the ecliptic into 12 segments or "signs" of 30 degrees each, then this didn't become standardized in Mesopotamia until about the 5th century BCE. The constellations themselves had already been established long before that though. Also, most of the qualities that astrologers associate with the zodiac weren't put into place until about the 1st century BCE.
So, to answer your first question, yes, the zodiac is about 2000-2500 years old. Does this make it one of the oldest conceptual images in human history? I'm not sure about that, but it sounds like a bit of a stretch. There is a lot of recorded history already before the zodiac shows up on the historical timeline.
I don't fully understand your second question, although maybe it would help if I pointed out that the constellations were established first, and then later the 12-sign zodiac was measured out later. You have to understand the the zodiac is not just based on the images associated with the constellations though, but it also incorporates other elements that have to do with the seasons, and this is part of the reason it doesn't fully match the constellations, even back then when the tropical and sidereal zodiacs were roughly aligned.
One last point that I want to make here is that I would be very careful about taking anything that Zeitgeist says for granted about the history of astrology. The purpose of the astrology section of that movie largely seems like a polemical attack on Christianity, and astrology just seems to be their access point for accomplishing that. As a result of that they seem to take a lot of liberties with their framing of the history of astrology in order to bolster their arguments. So, take it with a grain of salt, or some similar expression.
Do we think that the image was modeled after what we saw in the sky or could is there a possibility that the image was created before the heaven was catalogized?
By this, I assume you are suggesting that ancient astronomers, seeing the utility of breaking the ecliptic into segments and naming them, then superimposed these segments on the sky. To a small degree, this is true. Mainly, as /u/TiberiusRedditus says, the constellations were already named and they just got organized into the Zodiac. Some of them, such as the Twins or the Lion, are very salient celestial features and they were probably among the first named. Alexander Gurshtein has proposed that only the four cardinal constellations on the equinoxes and solstices were named at first, and this was updated thousands of years later because precession moved the spring equinox out of Gemini and into Taurus. At any rate it is true that they were regularized into 30 degrees each, which is done for convenience and because it pleased their Pythagorean aesthetic sensibilities rather than from any a posteriori motivations.