Using fastmail in its web interface:
1, Make sure you are in HTML mode, and compose the text of your email as usual
2. Post your image on a publicly available but private/hidden website, I recommend Google photos aka Picasa albums
3. Leave the cursor where you want to insert your photo, and switch to "raw html".
4. Looking at your photo in your Google album, choose "Large 800px" in the "Embed image link", and copy that link ( click on <table size>="width auto .. and copy to your clipboard, ie right click, 'copy')
5 Paste that code snippet into your raw html message
6 Click on "Preview" to check how your email will look like
7 Send - Voila !
More details
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
a- To help you test & practice, here's one example of the raw html in step 4 you can use (copy and paste as is)
<table style="width:auto;"><tr><td><a href="http://picasaweb.google.com/lh/photo/lj1RVubAHil1WbUdd45wRg"><img src="http://lh4.ggpht.com/atchen/RyDe7Ge30WI/AAAAAAAAADU/Y8s5VRHRzLA/s800/IMG_0703.JPG" /></a></td></tr><tr><td style="font-family:arial,sans-serif; font-size:11px; text-align:right">From <a href="http://picasaweb.google.com/atchen/Snapshots02">Snapshots</a></td></tr></table>
b- for Step 1, in order to see the "raw html' option you have to click on "advanced" ..
c- for Step 3, you can see where to leave your cursor by locating your words amidst the html jumble .. in between two <br /> is fine