My parent policy handbook states:

"Parents give permission for their child to have their photograph taken or be videotaped, and for those photos to be displayed in the child care home. The parent will acknowledge that their children my be in a photograph or videotaped with other children, and on occasion these may be exchanged with other parents."

In my contract that parents sign, it states:

"I give permission for photographing and videotaping for purposes described in the parent manual." Then parents circle 'Yes' or 'No'

I also ask the parents to not post pictures on Facebook or share via email any pictures that contain other daycare children (of course they can do as they like if it is only of their own child). When I email group photos I also include a reminder that these photos are only meant for personal use and not be shared.