I believe people quickly know what works and what does not, even without directly being aware of it. If a woman wears a new type of lipstick, the signs that it is working or it is not working are very subtle, but over a few days, she will understand that it's not working. She will then change to one that works a little bit better, and when she tries one (recommended by a friend) she will see other subtle signs it works.<p>It's the same with profile pics - the girls cycle through many different pictures and there are subtle vs not so subtle signs that a picture works better than some other one.<p>To be introduced to that particular style, one has to see it somewhere, and as it becomes widespread, you get to see it more and the chances of you trying out increase.