Image via CrunchBase
If you do not opt out of this "feature", your photos will appear in FaceBook ads hawking whatever product or service making it appear a bit like you recommended it to your friends.
Here's How you Can Turn Off Your Pictures in FaceBook Ads
To opt out of this "feature", go to "Settings" (top right, next to "Logout"), select "Privacy Settings", select "News Feeds and Wall", and select the "FaceBook Ads" tab. Set the "Appearance in FaceBook Ads" to "No One".