tinkerbell, you can get the image URL if you found it on the web and put it inside IMG tags (or click the little landscape icon in the post editor and enter the image URL there, which will put it in tags for you). If you uploaded it from your own collection you can click the thumbnail and copy the URL, then put it in IMG tags.
IMO a good Haight avatar has to combine detachment, ironic self-effacement (because he really thinks he's pretty awesome, and he is), double-ironic self-puffing (because it's designed to look like self-effacing facetiousness but it's actually all very accurate), quirkiness, and curmudgeonly goodwill. The Haight is a man of many layers. This does not mean Shrek would make a good avatar for The Haight; it would not.