Stop reading if you don't want the story ruined. There's a fair chance it could be.
ADDED 5/12: Latest here "Space Jockeys are Galactic Police"
Here's the new (loaded) image we got this morning.
I just posted my theory on the human in the painting (link above). Now, let's look at the other figure (to the man's right).
This is a Space Jockey. Its placement in relation to the man and its body language reveal quite a bit about Space Jockeys in general and the 'Prometheus' backstory.
Here's the latest shot of SJ we have.
In my opinion it's a woman. I had thought she, along with male SJ, were on their way to colonize Earth. Looks like I was wrong.
Notice the circled part. See the spike coming out of the elbow? There are two such spikes in the arms of the figure next to the man in the painting. Here's a marked up version of that crop (with contrast boosted):
1: The head, with similar shape and features as the SJ
2: Right shoulder, with ribs similar to features of the SJ anatomy and ship design
3: Right elbow, with spike barely visible
4: Right knee
5: Left knee
6: Spike coming out of the left elbow
The figure next to the man has to be a SJ. There is nothing else that we know of that it could be.
Why would a SJ be cowed next to a human especially considering the man is being attacked by one of the weaponized organisms in the horseshoe ship which the SJ are piloting?
Looking at the SJ's posture it's clear he/she isn't happy. It's certainly not the proud conqueror as I thought this morning. In fact, the SJ isn't even standing. It crouches, and its head isn't just lowered, it's between the knees with the arms wrapped around the knees in an effort to hide or disappear. What would that indicate? Shame. Fear. Guilt.
The SJ in the painting is filled with self-loathing. It is at the man's feet as if to beg forgiveness. Why? Because of what is happening to the man. Because there is a parasite on the man's chest about to kill him and, presumably, the SJ is responsible for putting it there.
What could that indicate? Why would the SJ kill a human but feel guilty about it? The only reason possible is that they are doing so against their will. They have been directed to kill humans and have no choice in the matter. They are slaves and executioners serving some master and they hate themselves and what they are forced to do.
Considering this, the SJ were not on their way to Earth to colonize it for themselves, but were coming here to clear the planet of humans so a Master Race (MR) could take over the planet. Then, presumably, the SJ would perform all menial labor while the MR lived in luxury.
I don't think there could be another way to explain the way the SJ appears in the painting.
The weaponized organism is the device of choice of the MR to eliminate intelligent life from a planet so they may take it over, and the SJ are the slaves who carry out this work. They, the SJ, travel to a planet to make a survey of it and determine whether the MR would find it desirable. The SJ make many such trips over the course of years or even centuries. During that time their visits are depicted in works of art by indigenous people (like those in the trailer found by the archeologists in the caves). Once the planet has been found to be acceptable the SJ return with the face-huggers or other such weaponized organism and wipe out the indigenous population. Once this is accomplished the MR arrive and claim their prize and the SJ go back to being everyday slaves.
That would explain the SJ's dejected demeanor in the painting. The photo is still part of a trophy gallery but it belongs to the Master Race not the Space Jockeys. It is an account of all the civilizations the MR have destroyed. The gallery is there not so much to inspire the SJ but, rather, to remind them of their wretched place in the order of things. These paintings serve to demean the SJ and glorify the MR.
So, who is the Master Race? Will we see them in upcoming stills? Wouldn't think so. That's got to be a reveal best saved for the movie. But, thinking about it, I wouldn't be surprised if we only see them in the ceiling painting in the trophy gallery (hit links at top for explanation), right in the center, gazing at all their victims.
I kind of hope we don't get any more stills from 'Prometheus'. I'm worn out. On the other hand, considering the story possibilities, I'm looking forward to a sequel to 'Prometheus'.