There has actually been quite a lot of academic research on this.
What's generally been found is that the more a face conforms to a statistical average, the more attractive it is deemed to be on average. In evolutionary biology, this is referred to as
assortative mating, where potential mates will naturally look for characteristics which are common within the population.
Researchers at the University of Glasgow founded a
face research lab, where they compiled thousands and images of people from different countries, and they digitally merged them together to create an average composite. The results were as follows:
Average male face:
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Average female face:
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What the researchers found is that with each of the images above, the faces were deemed in surveys to be "more attractive than average", despite them literally being the average.
Another interesting way of measuring beauty is with the golden ratio, which is where the ratio between two quantities is equal to the ratio between the total sum and the largest quantity. See the compilation of rectangles below:
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The interesting thing, from an observational standpoint, is the frequency with which this appears in nature:
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To see if this has any relationship to beauty, some researchers have attempted to find out if faces which conform more heavily to the golden ratio are deemed "more attractive" on average than faces which conform less heavily.
I believe research is still ongoing, but in numerous studies of celebrity faces, two people who's faces have been found to conform almost perfectly to the golden ratio are actor Jensen Ackles:
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and actress Amber Heard:
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Personally, I think there may be something to this standard, since they both strike me as incredibly attractive.