Is there a way to delete orphaned image (media) data?

This feature is available only when ACLs are enabled. You can assign the DELETE permission to users allowed to delete Mediafiles. They then can use the delete button in the media manager popup or the Delete button on the View tab of the third pane of the Fullscreen Media manager.

Deleting media doesn't free up space, it actually moves them to the “media_attic” if mediarevisions is enabled. See also maintenance.