I find that Terragen has this unusual white glow about its images, it has a limited amount of colors and there is usually no definitive black. So, postwork in PhotoShop is usually required. I would darken the black, adjust the other colors and turn the contrast up by atleast 7-9. Below are a couple links of images I have created with Terragen. You will see where PS was needed.
i think it's very realistic. i can envision us living in this location someday... although i think you could improve the clouds and it would be without question exactly like a photograph.
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i almost put a lens flare in the render with photoshop but thats so noob and i cant let myself sink that low