Permission to post photos on social sites?

Hi there,

We have lots of gorgeous pictures from wine events that feature visitors and customers both in the foreground and background. My gut tells me the right thing to do is to contact these people and get their permission before flinging their images out onto the social web ... even though we wouldn't "tag" or name them in the captions.

How do you handle posting event photos on social sites?

Thanks!
Catherine Thorpe
Adastra Wines - adastrawines.com
Ed's Red - edsred.net