PhilO still seems to be having some trouble, given his post on the "Show us your Whistle Collection" thread.
PhilO, once you have the image open in Facebook:
*In Internet Explorer, right click the image and select Properties
-Select all of the text in the "Address" field, from "https" to ".jpg". Dragging your mouse while selecting will enable you to move to the top or bottom of the Address field to select from the beginning to the end
*In Chrome, right click the image and select "Copy Image URL"
Use this entire long URL within the Img tag to post the url.

A couple more tips:
You can use the "Preview" button to view what your post will look like to others before clicking the "Submit" button to ensure it is properly formatted.
Additionally, you can click the "Edit" button in the bottom right hand corner of your post and edit it if you need to make changes, so that you don't have to make multiple posts. However, the ability to edit a post expires after so long.
EDIT: I like imgur.com, which allows you to upload and link images trivially without needing to register an account. This makes it great for sharing, but less great for archiving your personal images, where photobucket would be superior.