For this specific drawing: Robot City. I started with different photos. I used the perspective angles that was already in the photos. That's why it still a sketch, because the photos helped me concerning background issues.
Ah, I presumed so. I think photomanipulation is more like taking stock images or textures and simply pasting them into an image with some alterations here and there.
This, being a "sketch", as you say, was hand drawn, right? (digitally, of course) A drawing is still a drawing if you used photos as references, and even guidelines or initial overlays. But as long as, and it sure seems so here, that the end result is every stroke you placed yourself, then it's more than just photomaniupulation! :D
As you say, photomanipulations are not welcome most of the time, I guess because it's seems to be lazy and not creative.
But unfortunately, (sorry if I disappoint few people) as a professional digital matte-painter, I use a lot of photos in my work. It's always photos taken with my own digital camera for my specifics needs.
Because the main source light in this image is the eye of the robot and not the sun. I think it's logic to see the drop shadow of the human in this direction while the drop shadow of the robot goes in an opposite direction. But again, it's a quick sketch, there might be some mistakes.