Well there's an Easter Island head from Gradius, but that's not what you're talking about.
Damn, I never noticed that!
But, it's in the "close-up pic". So it focuses only on the one painting.
HINT HINT HINT: It's not hidden, or obscure, it's in plain sight, and, personally, it's something I noticed right away (because it is unusual). Also: SEGA!