You have to upload a pic via User Control Panel. Click on the Profile tab, then Edit Avatar on the left panel.
You can either upload a pic from your computer or copy/paste URL from a website picture, but the dimensions cannot be bigger than the following: width - 100 pixels, height - 100 pixels, file size - 16kB.
the upper left hand corner there is a button that says "User Control Panel"
Then there will be tabs: Overview, Profile, Preferences... Click on "Profile"
Then on the left there will be more tabs: Edit profile, edit signature... Click "edit avatar"
Then just browse through your pictures and edit the size so it's 100px X 100px and upload
Hope that helps, let me know if I left out any steps.