Not sure about a profile picture but to post one there are two ways.
From the web - copy the URL (right click mouse and select properties, hi-light and copy the URL address shown). Then on the left side of this screen Select 'Insert Web Image' and it will be posted.
If the picture is on your computer - attach image below. Browse for the picture from you computer and the image will upload to liweddings and post.
If you post from the web you can add multiple pics in one post. If you upload them from your computer I think it's only one a time.