Due to the change in 50be048ad0cbe0e9150ca2351b894b041ae7cf49, image display specifications like
#+attr_org: 300px don't work. From the commit message, it looks like the intent was to ignore specifications like :width 4in. I'm not sure if ignoring "px" specifications was intentional. If this is not a bug and width should be specified as an integer (i.e. 300 instead of 300px), then the manual needs to be updated. In (info "(org) Images") I still see examples like #+ATTR_HTML: :width 300px -Karthik