If you are taking pictures of your community events and posting them on Facebook, for example, you need to get approval from the residents! I've heard that you can post announcements at the door that pictures will be taken during the event, and by attending, you are giving permission to post those pictures. But I don't know if that is legally correct.
There are a couple of ways to handle this. Have a model release form in your leasing packet and have it signed by the residents at time of move-in. Also, when you are having an event and you know photos will be taken and possibly used in press releases or posted online, have a stack of release forms available for residents to sign.