Below are two major communities for sharing images under CC licenses. For more communities, see:
Flickr is a popular photo- and video-sharing site that has enabled Creative Commons licenses. The easiest way to post images online with a CC license is to let Flickr handle all the hosting, posting, and licensing for you.
How to publish on Flickr
Wikimedia Commons is a media file repository of CC-licensed and public domain images that supports Wikipedia articles and other Wikimedia Foundation projects.