They're called "Avatars", and this is how to post one:
Go to "Profile" up at the top of the page.
When that page is open, look at the menu on the left, and select "Forum Profile Information".
Now you'll have a page that allows you to choose or upload an Avatar.
Avatars can be up to 100 by 100 pixels in dimension.
Supposedly, if you tell the software a picture to use via URL (like one from your Gallery Album), it will create an Avatar from that picture.
Try it and lets see how it works.

PS - You did a fine job with your pics in the Gallery, Ice.
