The image called a profile picture is displayed only on your profile page. The one that's displayed in the left margin next to all your posts, PMs, etc., is called your avatar. For example, my profile picture is a tarot card; my avatar, which you'll see at the left (unless you have avatars disabled) is a cat with a bug on its nose.

There's one link on the Your Control Panel page for uploading a profile picture and another, about six lines farther down, for choosing or uploading an avatar.

Hope this helps.