How do they go about judging recognition? Who keeps score? What combination of media? I'm sure it is more than 10 people in a room being observed? Interesting.
This is simplified but to give you a general idea.....
Selecting celebrities for major ad campaigns is usually measured with market research -- most often with a carefully designed survey and/or 1-on-1 interviews.
>> The brand attributes of celebrities are measured in the same way as brands.
By recognition and awareness -- I mean do the target consumers recognize the image of the person? -- are they an "icon", a symbol. How rapidly do they recognize someone?
Awareness is measured by asking representative consumers general questions to measure unaided awareness -- example, name a brand of soda? Coke, Pepsi..... (The order matters). Then prompting for more -- can you think of any more soda brands? 7up (secondary unaided awareness) Then asking about missing brands? Have you ever heard of Dr. Pepper? Yes. (aided awareness.)
Then there are questions about familiarity, associations, attributes...
For celebrities, there are also background searches and conflict reviews.
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There are also some syndicated research tools the most famous of which is Q Scores.
en.wikipedia.org/wiki/Q_Score