Which Celebrity Doppelgängers Do not Look-Alike Actually?

Many celebrities look similar to each other like Dean Morgan and Javier Bardem. 

But on contrary, some celebrities do not look like each other like Leighton Meester and Minka Kelly. Most of them can not be regarded as each other’s doppelgangers. 

And I do not get why Isla Fisher and Amy Adams are called doppelgängers by people. Yes, both of them have the same red hair and fair skin. But apart from that, they do not look alike in any way.