The goal of this issue is that when we deprecate plugins and APIs and introduce a forward between the old modules and the new ones (to keep backward compatibility) then these forwards should apply in all cases, and in particular in the ImageGraph plugin.
Currently the graph generates an error: http://demo.piwik.org/index.php?module=API&method=ImageGraph.get&idSite=3&apiModule=UserSettings&apiAction=getBrowser&token_auth=anonymous&graphType=horizontalBar&period=month&date=today&width=500&height=250
Invalid API module and/or API action
(out of scope: later we could add an integration test case for it in #6864 )
Btw it can be seen on the following developer guide where the resolution graphs are used as example http://developer.piwik.org/api-reference/reporting-api-metadata#static-image-graphs