I saw some exceptional work of an CG-artist the other day that really made my jaw drop.
If i recall it right, he called it 'Matte painting'.
With the new CS series, you can bend and morph your photographs into the right shape.
I use this tool often to re-adjust shapes ive made myself.
But with photo's, like that of buildings, you pick out small pieces and photomorph it into the right shape as texture for your giant alienships.
I'll start using it myself now, but only for the purpose of adding more structure to the ground or things like the dragonskin.