From one of my friend's feeds:
"Facebook Ads" is the last tab on the right at the top of the "Account Settings" page. WHen you go to the "Facebook Ads" page, there are actually two drop down menus: one for third-party ads and one for Facebook ads. Make sure you choose "no one" for both.On Friday March 18, Facebook will start using your photos in ads that will appear on the profile page of your contacts. It's legal and is mentioned in the fine print when you create your account. TO stop this do the following: Account, Account Settings, Facebook Ads. Choose "No one" on the drop-down menu and save changes.