Those instruments look too realistic compared to everything else. Since both guitars and bass are flat-facing, I think that they were pictures and then pasted into this with minor edting.

Yeah, but other than the copy/pasting, this is the only k-on picture that has an accurate depiction of the instruments used. 1:1 in scale, shape, texture, and trademark logos.

Either way, the cap on Yui's Les Paul is gorgeous. Look at that finish, I mean it looks like it was made in the custom shop.