For whatever reason, that web address you pasted in was shown as a web link not an img link. When you have the image uploaded and you copy the link address, then at the top of the posting window, click the yellow square button for "insert image". Paste the link location you just copied into that space. When you submit your post, this will insert the pic full size and still have it at the bottom of the post as a thumbnail.

Here is a screen shot showing the "insert image" button: