My first thought was that it may well be a well-faked composite image, but that occured to me mainly because I'm somewhat familiar with the tools of image manipulation.

The lack of any noticable film grain in the image, I felt, was a strike against it. Certainly not decisive, but if the original information is digital it'd be much easier to manipulate...you don't have to worry about matching film grain patterns in different parts of the composite (which isn't an impossible task, but adds complications).

I too thought something was odd about the lighting, and tried to examine shadow angle and length, but didn't come up with anything useful. The patterns of light around the "doorway" also didn't seen right to me, but without knowing the reflective particulars of the materials involved, it's just a feeling.

If it's a fake image, it's a decent one, imho. But it's really not nearly as sharp as it could be. If the original image were photographic (as opposed to digital), it'd have to be pretty hi-res in order for the film grain patterns to be sub-pixel. And if it's digital, why are we getting a version that's only some 89k in size? The caption notes that the image is from a floppy, which can typically hold almost 1.5 meg. Why only 89k? My suspicious side says "Camera motion isn't the only way to blur an image." The pic is just clear enough to make it stand out from the crowd, but not clear enough to really convey a lot of information.

As for the saucer itself, I wondered if it was a 3D graphic. If so, it's a very simple model with a fairly good texture map, and probably a reflectivity map as well. The maps alone would probably be several meg in size as they show no obvious signs of pixelation. The background sure looks like the real McCoy to me. If it's a composite, it's a skillful one, imho. As Tom suggests, there's a lot of good software out there for creating photo-realistic images. An artist with talent and a devious side would have no problem producing an image like this over a weekend.

Have you seen the short film "405 The Movie?" It was produced by a couple of talented guys with commercially-available software and some time on their hands, and the results are pretty convincing.