Here are the instructions you need to unlock/relock your pics:
Unlock - click the “unlock” button on that member's profile. To unlock your private pictures for all your buddies, go to Buddies > Unlock List and click the Unlock Pictures for All Buddies on the bottom of your page.
Relock - If you want to relock your pictures for a specific member, go to Buddies > Unlock List. From there, you can view everyone for whom you have unlocked your pictures. Simply click the Lock link next to their screen name, and your pics will be relocked for that member. For a quick relock of everyone just click the Relock All Pictures on the bottom of that page.