This is an icon:
Those are four distinctly different faces presumably from four different actors/models. Yet show any one those pictures to anyone, anywhere and he or she is going to immediately know who it is.
The second is probably the most ubiquitously familiar
; that does not make him the most iconic
I bought a friend of mine a TOS cast t-shirt because he loved TNG. Loving my gift
he took it away on a holiday to climb the Himalayas where he would be camping and staying in huts without running water and electricity.
He came back and he told me that he was amazed how many people recognised the people on the shirt. In places without TV or movie theatres where they didn't speak English, people would come up to him and say 'Kirk', 'Spock'.
So you claim they're not icons but a lot of people around the world recognise them.
Aside from being an anecdote and thus proof of nothing, this gives no indication of how many people walked by who had no idea who they were.
Non the less, note they said "Kirk" and "Spock" not "Shatner!" "Nimoy!"
Dollars to donuts, your friend could paste Pine and Quinto's faces onto said shirt and get a similar reaction.
Also, I wonder if, had you given your friend with a picture of Shatner and Nimoy drinking cocktails while wearing 70s leisure suits, he would have garnered the same level of attention?
Poor examples. As cartoon and comic book characters, respectively, Mickey and Superman were subjected to numerous changes in their early years--there was no hardline, established look in the way the right actor immediately shapes a role with traits that are not always born of the screenwriter's pen. The Superman of Action Comics #1 was already altered by the time AC#6 or 7, where the "S" chest emblem took on a new look, alternated outline colors, along with the color of his cape emblem.
Here's a challenge:
Take stills from the Fleischer cartoon and MoS and walk around public asking "Which one's Superman?"
It is the actor's lightning-in-a-bottle shaping of a character which makes a cultural icon. They are not pick n'n swap parts like that found in so many reimagining/reboots to follow. The very reason the nuTrek actors--with all the money and marketing in the world--are not in the same position, two movies in.
Can you even define "icon?"