This is what I mean and it may be very hard to do but here goes.
When a user 1 signs up and setup there profile they don't upload a photo or just make them private.
So now another user 2 sees a possible contact with this user so on that users profile an image from the system says
ASK USER FOR THEIR PHOTO. That is the blank photo asking this, so user 2 now clicks on that photo and the system sends user 1 a request from user 2 that they would like to see a photo of them, so user 1 now can look at user 2's profile and decide whether or not they want to let user 2 get a photo. So now user 1 can be friends with user 2 to allow to see private or upload a file and that file can be private or the default one now.
Maybe this can be done now just by adding a link under the photo stating this and it could be just a private photo. Again this might be something too much I don't know.