I am trying to use the wikimedia API for wiki commons at:
http://commons.wikimedia.org/w/api.php
It seems like the commons API is very immature
see page: http://www.mediawiki.org/wiki/API:Meta
You can use foreach image the tag 'meta=siteinfo' and the tag 'siprop=rightsinfo' (siprop is the prop of the siteinfo) Then you will see the rightsinfo of the picture.
In your case of Brad Pitt it would be like:
http://en.wikipedia.org/w/api.php?format=jsonfm&action=query&titles=File:Brad_Pitt_at_Incirlik2.jpg&prop=imageinfo&iiprop=url&meta=siteinfo&siprop=rightsinfo