I did it! I did it!
For Mac nerd reference, if you need to replicate what I did, download Firefox and log into your Blogger account from there. Then post the image you want to use on a flickr account (could work with Yahoo for all I know - they just were not working when I needed them to be) and then right click on the image in Flickr and choose Copy Image URL. Then go to Edit Profile in Blogger and paste this into your Photograph details on your profile page. Save changes and it SHOULD work.
Just to celebrate, here's another photo from my flickr collection... a jet trail in the sky over The Chellah at Rabat.