I don't think it's particularly selfish, people are just unaware that there's a boundary. To them, they're doing something nice, they don't know any better.
They're not exactly aware that a certain level of relationship has to be formed first before that becomes okay. I've had close friends and family send me portraits of myself and I found it sweet because they're allowed to. However, if a random person does the same thing I'll find it creepy.
It's the randomness (creepiness) that bothered me as much as the fact the ill-mannered fellow didn't care to ask permission despite it being so easy to do. You're right too, there's people who could get away with such things,but a person should never assume they can, unless they know.