I have been trying in vain to get this working but maybe there is a workaround.
The image element only allows for images coming from the media library or upload.
So I added a code element and added the following html:
When I try to save, it always complains that there is an html error and will not save.
It works fine in w3scools tryit editor... so I know the code is ok. http://www.w3schools.com/html/tryit.asp?filename=tryhtml_basic