You might not be aware of this (I wasn't). If you add an image in Atto, then "delete" it again in the editor you only delete the link. The actual file remains. You can see the files by clicking the file manager button on the toolbar.
Now these can mount up in a big course. We hit on it using Ally - it reports on a load of files that you thought you deleted.
Has anybody seen a plugin, got a great idea and so on.... thoughts about handling these files?