So there is an issue we need to address. After sharing a couple of the recent Top 10 country photo posts from WLM 2011 on Facebook, I was gently reminded about an issue that has come up already with CC-BY-SA licensing and Facebook. The Wikimedia Foundation Legal and Community Advocacy department wrote some guidance on this matter (not legal advice, but an attempt to clarify):

For the applicable section of CC-BY-SA, see 4(a) and 4(b) here:

The relevant part of the Facebook terms:

"you grant us a non-exclusive, transferable, sub-licensable, royalty-free, worldwide license to use any IP content that you post on or in connection with Facebook (IP License)." https://www.facebook.com/legal/terms

Essentially, if you upload your own photo, you have the right to grant multiple licenses, so you would be fine. But as the guidance notes, if you're uploading others' photos, you don't have the right to grant a license. These Top-10 galleries are very nice, but they are also likely not a good idea with the way Facebook sub-licenses. I'm going to stop sharing these galleries on the Wikipedia Facebook page for this reason and start pointing to the Commons page where they are all listed:

I won't give others advice, since IANAL, but at a minimum, every WLM photo should be properly licensed, which means that it must have a link to the actual CC-BY-SA license page. For example, this photo is not quite licensed correctly. 

In addition to the name of the author and the license text, it must have a link to the CC-BY-SA 3.0 Unported license page here:

For example, this one is missing all the necessary licensing info:

Arguably these photos probably shouldn't even be on Facebook like they are, but again IANAL and I'm not giving you legal advice. That's a decision for you all to make.

thanks,
Matthew