i think if you post a pic and set it to friends only can see it and someone shares it then anyone not on your friends cant see it... if that makes sense
i have 2 facebooks... one i rarely go on that has family and real life friends plus online friends that is all friends only and another that ive had years that is a mix of public, friends only and also stuff shared with specific people on my friends that other friends cant see....i can see the point of view from both sides, i have loads of photos on fb but if i had joe bloggs down the road on my friends then he would be blocked from seeing them as i wouldnt necessarily invite him up for a cuppa and look at my holiday pics