In reply to Will.

Will, yes I believe I uploaded them to my own website first, and then I put the URLs for them into the "icon" field. (Note that you might have to click on the "more settings" option in the Inoreader interface to see the field for the icon.) I've mentioned micropub to the developers of Inoreader and hope they'll add support for it sometime soon. If you get a chance, email support, tweet, or otherwise contact them and suggest you'd like micropub support too. I'm sure the more demand they've got, the more likely they are to add it.