[e] (0) Clarify what it means for an image to have an origin
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=23930
Affected topics: Security

git-svn-id: http://svn.whatwg.org/webapps@8320 340c8d12-0b0e-0410-8428-c7bf67bfef74