Your URL doesn't point directly to the file.
For example the one above is http://imagescas9wkkv/ which isn't valid.
The easiest way is to right click on the image you want, choose properties and copy the URL.
Then click on the attachment icon in the advanced editor, paste the URL in the 'Upload file from a URL' box and click upload.
You can then insert the image wherever you want within you post by clicking the attachment icon and this time selecting the uploaded file.