Choose the picture you want to restrict access to. At the top of the picture,next to your FB name will be a box with a drop down menu -click it and it will say "edit post privacy".Click this and it will take you to the original post the picture was in on your timeline. Again click the box under your name and choose "more options" then "Custom". A box will appear and you can physically choose who share this with, or perhaps more importantly who NOT to share with, by inserting their name in the appropriate box.