Can't see the Winglet, otherwise it would've easily confirmed type of a/c.Yeah wings look similar to C-17's. So I don't recall any C-17 with refuelling boom.
So it looks like escort
The picture is taken above the wing which indicates it is a mid-wing aircraft hence KC-135. C-17 is a high wing aircraft with no windows above the wing. The two aircraft have different power plants and the easy way to tell the difference externally is that C-17 engine nacelle (cowling/cover) have these vortex generators (fin-like structures) on both inboard and outboard side of the inlet which would have been visible in a shot like this.Can't see the Winglet, otherwise it would've easily confirmed type of a/c.
And yeah, C-17 (Globemaster III) doesn't come in a Refueling variant - as cool as an idea that may be.