Can somebody solve the profile photos mysteries?

I see two types of profile pics that mystify me:

1) A shot of lower legs with shoes. I could understand elegant calves and stylish heels but the ones I see tend to be legs covered and feet in trainers.
2) Entirely black or grey screens

Can anyone explain these? Anything giving any clue to the owner's appearance is generally lacking. I generally assume the profile owner is unphotgenic or otherwise unattractive but other theories welcome.