Anyways, I'd argue that's the most comprehensive database of CC-licensed works.
Also, I just checked that flickr.com still allows you to filter their searches by license.
(see https://en.wikipedia.org/w/api.php?action=help&modules=query for reference)
edit: formatting
I notice a slight difference between
https://commons.wikimedia.org/w/api.php?action=query&generat...
and searching for 'cat' on canweimage.com
Is there some query processing needed?