Hey, thanks for pointing that out, because I had same dilemma.
Well, I could but I'm not sure if it's necessary. Am I obligated to mention all thing that inspires me and is this concept unique to this artist? Also, this image inspired me too:
I don't like using someone's concept, but in this case it's just a guy sitting in a spaceship. It's not like I made same image, some credit belongs to the client too. Does it matter that much?