Thithi,^ I didn't know that!
Here's some steps:
1. Click on the link below the quick edit screen:
2. Will take you to full page edit mode where there are two areas to add additional pics:
3. If you click on the small landscape box(rightside of the above photo, see red circle), it will take you to an additional box where you add the link to a pic if it's already uploaded onto another website(photobucket, webshots, tinypic, etc):
Save when finished.