Musk....

Compare his physical size/build as seen in his cameo in IronMan 2 with the guy that is presented as 'Musk'... sure you can pack on muscle/mass but a slender and scrawny frame doesn't suddenly become broad shouldered and big-boned....

People keep looking at the surface but aside from muscle/sinew attachment-points/angle what people should look at is underlying structure as a whole, surgery can do a lot but the only bone changes that can really be done is to the chin, you can't re-profile someones cranium shape or reposition eye-sockets, nor can you change the eye/nose/mouth geometry.

When you start looking at minute details you tend to not see the forest for all the threes, take in the general whole and you will easily see what details that stand out....

edit: also, facial expressions are very much dependent upon underlying structure as well as muscle/sinew/cartilage positioning and geometry, this is usually how people suddenly recognize a person that they haven't seen in years and that have change a lot with age, that one expression that remains the same no matter how much someone has aged, and with the people that are replaced you have rather a lot of examples to compare and if a similar facial expression looks radically different(like a smile or a furrowed brow) then chance are, it is not the same person...