TD,
The Header to an attachment in a message Composed in Plain Text, in Mail, will still have Content-Disposition: Inline. In general this does not impact whether the recipient's email will provide Inline View (what Apple calls View in Place). It does, however, impact Lotus Notes which attempts then to render Inline, but fails miserably. (Interestingly, Lotus can Forward the message in good order to others.)
The Mail plugin, Iconizer, changes this header to no longer have an inline disposition, but this does not prevent email clients such as Mail from rendering to View in Place. It would prevent the error in Lotus.
As others have said, the fact that an image will View in Place as you are composing, or in a received message, does not alter their status as true attachments.
Ernie
Message was edited by: Ernie Stamper