you're getting some terms mixed up. the hub is the center of the wheel. the spokes attach to it. it may have a freehub body that a cassette slides onto (in this case the ratcheting mechanism is in the hub), or it may, like the bike you have pictured here, have a freewheel, which is a single piece that contains all the rear gears and the ratcheting mechanism.
cassettes are held in place by a lock ring that screws onto the outboard side of the freehub body, the piece of the hub that the cassette slides onto (like the stock photo you posted -- which to make things extra confusing looks like lockring photoshopped into place over a freewheel -- but that piece in the center is what you'll see on a cassette). freewheels are all a single piece and will lack a lockring. generally 7 speed or less will usually be freewheels and 8 speeds or more will usually be casettes. exceptions apply.
you only need a chain whip to remove a cassette.