Your URL must point directly to the image. Most photosharing sites already have
(minus the space at the " class="img lazy">). It would appear like:
Thats what my case used to look like, by the way.
There is also an option while writing your post to insert an image. You can click on the insert image button and put in a URL to an image there. It's the blue logo next to the formatting options (Bold, underline, italics).