I have prologue, and these screenshots give a decent impression on what it looks like on my tv, ok?
You only get an accurate impression of the game when the snapshot is taken when the image isn't moving. The first picture is taken with the car standing still on the Fuji straight, with the brakes on. The second is in movement, but with the camera keeping the car steady in center. You can see that in the background, the alternate lines of the interlaced picture pull the graphics apart in two directions when capturing.
You don't see this happening on a normal TV because you can only see one set of lines at a time which makes the picture look steady and fluent on a normal TV, which after all only draws 30 full images per second, but makes it look like more by drawing 60 half images per second.
GT4 actually generates 60 full frames per second however, which you can only fully appreciate when you have a HD TV (Progressive Scan) and the game supports it. It is said that GT4 will in fact support progressive scan, and that would mean higher quality images would then be possible. If a capture card supports grabbing such images, a lot better captures can be achieved still.
Nevertheless there are capture cards which better deal with the alternative lines and can pull the image together to make them look better. A card like daan's does a pretty good job at this, I might get something like that again sometime. With the cheap cards, like I have now, it's a matter of timing and making sure you capture an image that doesn't move too much.
I think GT4 Prologue looks better than GT3 in many ways, although GT3 certainly doesn't look bad itself. But tracks like citta are just a work of art:
But I do want to add that the contrast of the hong kong picture is lower, so that will look less jaggy when (re-)scaled backwards. 
But the point was if this particular shot could be an in game shot, and I think I've made my point there. There are, however, other shots that I think are concept art. 
