A while ago I had figured out that you can get Apple's Mail.app to display an image in mail from you by setting the X-Image-Url header in your MUA.
It's easy enough with mutt to do so, just add a line like this:
my_hdr X-Image-Url: https://geeklair.net/~dluke/images/dluke.jpg
to your ~/.muttrc.
I wasn't sure how to do it with Apple's Mail.app, though.
Fortunately, Dan Wood figured it out and posted about it.
Cool.
Cool!