> Can someone use Flicker to link Avatars and re-size them if needed? I'm asking if I could do it myself, not for someone to do it for me, by the way.

You can put any URL in the avatar box. You just need to ensure that:

1. It's 150px by 150px
2. It's hosted on a website that lets you direct-/hot-link to the image
3. It actually links to an image, not just a page that the image is hosted on (common mistake)

I simply recommend <http://imgur.com> because I know it's a good service. If Flickr fits the bill, then that's cool too.