Flickr Creative Commons Search
Flickr advanced search http://flickr.com/search/advanced/
has three check boxes
- Only search within Creative Commons licensed photos
- Find content to use commercially
- Find content to modify, adapt, or build upon
that generate 4 CC search variations
- CC any http://flickr.com/search/?l=cc
- CC commercial http://flickr.com/search/?l=comm
- CC derivative http://flickr.com/search/?l=deriv
- CC commercial & derivative http://flickr.com/search/?l=commderiv
the later one is equivalent to CC-BY-SA