Tosh, the following reply came from another forum, don't know if it's of any help.
I came across a similar issue the other day, when I had to turn a couple of rosters that my wife had made in Appleworks into pdf, so as to mail them to her colleagues at school who all use PCs. One-page pdfs were visible as text (or more like a picture actually) in the mail, instead of just as an icon. There is an option in Mail to "show attachments as icons", but if you mail it off and check your "sent messages", they will be visible as text again, rather than as icons. Beats me!
Indeed, if anyone sends us a couple of photos as attachments, the photos can be viewed in Mail, instead of just being displayed as icons (which are a bit handier than photos to drag, from the mail message, to the desktop.)
(of course, if you have a couple of them to send together, you could always turn them into a zip file, but don't expect any further compression, as jpg's, just like mp3's or pdf's, are already compressed files)