here is my thought... if someone wants to rip a picture that isnt of you are anyone you know (besides famous people) they are either going to rip or they are simply going to save it and then go upload it... so wouldnt you rather get credit for the picture when they rip or have them take your pic/icon and you not know?
When it comes to pictures of yourself/family/friends ect... then a person should ask to rip it because 98% of the time people dont want their personal pictures on other's profiles!!