Pass the media entry off to the appropriate processing function
(for now just process_image...)
+ :param media_id: MediaEntry().id
:param feed_url: The feed URL that the PuSH server needs to be
updated for.
+ :param reprocess_action: What particular action should be run. For
+ example, 'initial'.
:param reprocess: A dict containing all of the necessary reprocessing
info for the media_type.
"""