This also would be controlled for by the tools the blog author used though—if a women has more friends, then they would also probably get more likes on all of the rest of their images. Not sure if posting more photos would drive the average up or down, but it would probably drive the "above the baseline" selfies in the same way.
More friends, but then the likes are not uniformly distributed with the increase of friends. Also more pictures means the "best picture" could be more of an outlier.
So best pictures might rise further above baseline for that person. That is, top picture gets 1000 likes, but most pictures get zero. Sort of like Zipfian distribution of words.
Anyway, these things are actually really hard to control for particularly because different types of friends/people have different effects on the likes. Now add to this cultural differences between countries/states/universities/rural-urban, etc.
I think the best method that is actually practical was the one okcupid did at some point with "my best face" where you rate a bunch of people's pictures and they rate yours. Then you figure out what pictures are good from the data.
If they kept the data for all these contests, it would be much easier to interpret in aggregate.
