Here are the instructions if you are using IE for your browser.... it may different with another browser.
Once you have loaded your image into the correct gallery, right click on the photo. A pop-up will come up; at the bottom of the list is "properties". Left click on 'properties' - this will bring up a another box. In that box is "Address/URL"... mine is located about the middle of the box. Highlight and copy the complete URL [should end in .jeg]. Close that box then go to the thread and click on the yellow box and paste the url into it.
Els... in IE, the the URL in the properties box is not blue. Also in IE when I click on the yellow box - the 'http' is covered in blue and when I do a paste, it erases the one in blue so I only have one http.
Hope this helps you.