In addition to the « Text is available under the <a rel="license" ... » code at the bottom of each page, users should have a way to add "rel=license" when they provide an external link for the license of a specific (pdf, image, video or audio) file.
For example the html of http://commons.wikimedia.org/wiki/File:Collage_of_Six_Cats-01.jpg is failing from using rel="license" where it should, in the syntax of the link to http://creativecommons.org/licenses/by-sa/2.0/deed.en
By the same token, the original authors of a Work distributed under a Creative Commons license ( User:Ragesoss (Sage Ross) for one image, Hisashi for 4 images User:多摩に暇人 for one image, Derivative work: Caspian blue in the example given above) should be described with
in the links to their user pages (on Commons or on Flickr)
See the source code of http://labs.creativecommons.org/2011/ccrel-guide/examples/multiple_textimage.html or, for example, that of http://www.flickr.com/photos/60223652@N00/2677272571/ .
It seems that without such changes, the http://openattribute.com/ tool can't work fine on Commons (while it works fine on Flickr).