The photos are meaningless. They don't say which model year it is, nor does it say what the difference between the two photos is, if any.
That's why you look at the photos and see that the new one has a tapered base and the old one doesn't.
( a fact that one has to make up)
The New iMac Appears to have a Rubber Foot of some Kind (Not Sure if the Old iMac had this, its not visible in the Pictures, and i've never looked under the foot of one) aswell.